2013-03-23 15:14:53 +01:00
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# The Young Person's Guide to Programming in Minecraft
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2014-01-01 16:30:12 +01:00
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## Table of Contents
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* [Introduction](#introduction)
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* [Installation](#installation)
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* [Learning Javascript](#learning-javascript)
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* [First Steps](#first-steps)
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* [Variables](#variables)
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* [Functions](#functions)
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* [Building stuff in Minecraft](#building-stuff-in-minecraft)
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* [Common Block Materials](#common-block-materials)
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* [Dimensions](#dimensions)
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* [More shapes](#more-shapes)
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* [The Drone Object](#the-drone-object)
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* [Movement](#movement)
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* [Chaining - combining building and movement.](#chaining---combining-building-and-movement)
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* [Exercise - Build a simple dwelling](#exercise---build-a-simple-dwelling)
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* [Remembering where you started.](#remembering-where-you-started)
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* [Saving your work](#saving-your-work)
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* [Your First Minecraft Mod!](#your-first-minecraft-mod)
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* [Parameters](#parameters)
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* [true or false](#true-or-false)
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* [More fun with `true` or `false`](#more-fun-with-true-or-false)
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* [...and Again, and Again, and Again,...](#and-again-and-again-and-again)
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* [Counting to 100](#counting-to-100)
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* [Saying "Hi!" to every player](#saying-hi-to-every-player)
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* [While Loops](#while-loops)
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* [`utils.foreach()` - Yet another way to process Arrays](#utilsforeach---yet-another-way-to-process-arrays)
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* [Exercise](#exercise)
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* [Putting `for` loops to use - Building a Skyscraper](#putting-for-loops-to-use---building-a-skyscraper)
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* [Making Decisions](#making-decisions)
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* [Event-Driven programming](#event-driven-programming)
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* [Stop listening to events.](#stop-listening-to-events)
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* [Keeping Score - Lookup tables in Javascript](#keeping-score---lookup-tables-in-javascript)
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* [Counting block break events for each player](#counting-block-break-events-for-each-player)
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* [Next Steps](#next-steps)
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2013-12-19 12:21:55 +01:00
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## Introduction
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2013-03-23 15:14:53 +01:00
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Minecraft is an open-ended 3D game where you can build and craft
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anything you like. Minecraft can be extended and enhanced using 'Mods'
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(short for 'modifications') - additional bits of code that are added
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to the Game. ScriptCraft is one such Mod - it lets you program in
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Javacript right within the game, making it possible to ...
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* Build using simple javascript statements.
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* Extend the game in other interesting ways - add new Items, change
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the game behaviour and create mini-games.
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Minecraft can be played in single-player or multi-player mode (with
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friends). Most people play Minecraft in Multi-player mode where
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players connect to a Minecraft Server on the internet or locally
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(running on the player's computer).
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![Cottages created using ScriptCraft in MineCraft][img_cr]
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2013-12-19 12:21:55 +01:00
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## Installation
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2013-03-23 15:14:53 +01:00
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CraftBukkit is a version of the Minecraft server software which allows
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easy addition of 'Mods' and extensions to Minecraft. ScriptCraft is a
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'Mod' for use with CraftBukkit. Adding Mods to Minecraft can be
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difficult but CraftBukkit makes it easy. Follow these steps to
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Install ScriptCraft on your computer...
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2013-11-03 19:37:18 +01:00
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1. [Download and install CraftBukkit][dlbuk]. Then follow the [Bukkit Installation Instructions][bii].
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[bii]: http://wiki.bukkit.org/Setting_up_a_server
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2. Start the CraftBukkit server, then once it has started up, stop it
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by typing 'stop'. If you go to the craftbukkit folder (see step 1) you
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should see some new files and subfolders.
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2013-11-03 19:37:18 +01:00
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3. [Download the latest version of the ScriptCraft Mod][sc-plugin]. Then copy the ScriptCraft.jar file to the
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`craftbukkit/plugins` folder (This folder won't be created until you run Bukkit for the first time (see previous step).
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4. Start up the craftbukkit server again (see [instructions for starting the server][bii]).
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5. In the CraftBukkit command window type `op {your_username}` and hit
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enter, replacing {your_username} with your own minecraft
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username. This will give you `operator` access meaning you can perform
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more commands than are normally available in Minecraft. You should
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make yourself a server operator (Server operators have full privileges
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for the server) permanently by editing the craftbukkit/ops.txt file
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and adding your username (one username per line).
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2013-11-03 19:37:18 +01:00
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6. In the CraftBukkit command window type `js 1 + 1` and hit enter. You should see `> 2` .
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... Congratulations! You just installed your own Minecraft Server with
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the ScriptCraft Mod and are now ready to begin programming in Minecraft.
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Normally, Minecraft Mods are written in Java. This makes writing your
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own extension or game rules difficult because you must first learn Java.
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Java is different enough from Javascript. With the ScriptCraft plug-in
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installed, you don't have to learn Java, you can extend and customize
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Minecraft your way using Javascript. Javascript is easier to learn than
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Java but it's also more flexible and powerful and is used for creating
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interactive web sites and many other applications.
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2013-12-19 12:21:55 +01:00
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## Learning Javascript
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2013-03-23 15:14:53 +01:00
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To begin creating cool stuff in Minecraft using ScriptCraft, you don't
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*have* to know much JavaScript. ScriptCraft comes with lots of functions
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to help you create buildings of any size, and lets you experiment while
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you play. However, as you learn Javascript you will be able to create
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cooler stuff in Minecraft - not just buildings, you'll be able to add
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new rules and items to the game - even create mini-games for you and
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your friends. If you want to get started learning JavaScript, check out
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this [fun Javascript Tutorial][ce]. If you want to dive right in to
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ScriptCraft, read on...
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2013-12-19 12:21:55 +01:00
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## First Steps
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If you don't already know Javascript, don't worry, you'll learn a little
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about Programming and Javascript along the way. You've set up a
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Minecraft server and are ready to connect ...
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1. Launch Minecraft (keep the Bukkit Command window open).
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2. Click 'Multi-Player'
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3. Click 'Add Server'
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4. Type any name you like in the name field then type `localhost` in the
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address field. `localhost` is a special internet address that points to
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your own computer.
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5. Click 'Join Server' to join the craftbukkit server.
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6. Once you've joined the game, press the `/` key located at the bottom
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right of your keyboard. A prompt will appear. Type the following then
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press enter: `js 1 + 1` The number 2 should be displayed.
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... Well Done! You've just confirmed you can run Javascript code from
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within the Minecraft Console.
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2013-12-19 12:21:55 +01:00
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## Variables
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A variable is how you name something for the computer (and you the
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programmer) to remember. You create a new variable in Javascript using
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the `var` keyword...
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2014-01-01 16:30:12 +01:00
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/js var location = 'Blackrock Castle'
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... creates a new variable called `location` and stores the text
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`Blackrock Castle` in it. Now the computer has a new item in its memory
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called `location`. We can use that name like this...
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/js echo( location )
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... and the following is displayed...
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Blackrock Castle
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2014-01-01 16:30:12 +01:00
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...You might be wondering where the `''` (called double-quotes) went.
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When telling the computer to store some text, you have to put `'`
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(that's the double-quote character - press Shift+2) at the start and end
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of the text. The computer doesn't store these quote characters, only the
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text between them. The computer will store the variables while the
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Minecraft Server is running. Repeat the last command you entered by
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pressing the `/` key then the UP arrow key on your keyboard, then
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pressing enter. You can repeat that statement as many times as you like
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and the computer will always display the same value. You can change the
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value like this...
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2014-01-01 16:30:12 +01:00
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/js location = 'Mahon Point'
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...notice this time I didn't use the `var` keyword. I didn't need to.
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The `var` keyword is only needed when you first create the variable. Now
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execute this command...
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/js echo( location )
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...and it displays...
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Mahon Point
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Variables can be created and changed easily in Javascript. Along with
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the variables you'll create in your in-game commands and scripts, there
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are handy *free* variables created for you by ScriptCraft. One such variable is
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`self`, it contains information about the current player (that's you)...
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/js echo ( self )
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... displays the following...
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CraftPlayer{name=walterh}
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... for me but the message displayed will be different for every player.
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2013-12-19 12:21:55 +01:00
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## Functions
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ScriptCraft comes with a couple of extra functions not normally found in
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Javascript. These functions will help you build new structures and
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buildings which would otherwise take hours to build by hand. Before
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looking at the building functions let's look at the `echo()` function.
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`echo()` - as its name implies - will echo back at you whatever you
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tell it. For example, type ...
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/js echo('Hello')
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... and the game will display...
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Hello
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... type ...
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/js echo( 5 + 7 )
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... and the game will display...
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12
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... While you can now use Minecraft to help with Maths homework - I
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don't recommend it. Homework and Minecraft don't mix! The `echo()`
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function will display anything you tell it to - Text, Numbers and other types...
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/js echo( new Date() )
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... prints today's date. If the statement above looks confusing - don't
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worry - `new Date()` creates a new date object - I'll talk about objects
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later ...
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Tue Jan 08 2013 20:53:37 GMT-0000 (GMT)
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![Today's Date][img_echo_date]
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`echo()` is a very useful function but it is not part of the
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Javascript Language. You can't use it outside of Minecraft. There are
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many other functions in Javascript all of which you can also
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use in Minecraft. For example...
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/js Math.max( 6, 11 )
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... returns the larger of the 2 numbers you give it (max is short for
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maximum). While...
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/js Math.min( 6, 11 )
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... returns the smaller of the 2 numbers. That's another thing -
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functions can `return` stuff. You can store the result of a function
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(what it returns) in a variable like this...
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/js var biggest = Math.max( 6, 11 )
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... Now type...
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/js biggest
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... Not all Javascript functions return data but most do. As well as
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the functions provided to you by the Javascript Language and
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ScriptCraft, you can write your own functions like this...
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/js function whatTimeIsIt () { return new Date() }
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... Here you've created a new `function` called `whatTimeIsIt` and
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told the function it should return a new `Date` object every time it's
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called. You'll notice the above statement didn't actually do anything
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- it certainly didn't display the current time. That's because all
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you've done is is say what the function should do when it's called,
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you haven't called it yet. To call the function...
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/js whatTimeIsIt()
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... The current time is displayed. Congrats! You've just written your
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first Javascript function - you're well on your way to becoming a
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Minecraft Modder. There are many functions for working with Text,
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numbers and dates in Javascript...
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/js Math.random()
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... prints out a random number every time you call it. Try it! Then press
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the `/` key then the UP Arrow key to repeat the last statement in your
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in-game console. You'll see the number displayed is different each
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time. Think of Math.random() as a Dice with many many sides. You can
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rely on it to never return the same value twice.
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2013-12-19 12:21:55 +01:00
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## Building stuff in Minecraft
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2013-03-23 15:14:53 +01:00
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Now we get to the fun stuff - creating structures and buildings in
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Minecraft. Building by hand is fun but tedious when you want to build
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big - Towers, Castles and Fortresses. That's where ScriptCraft comes in.
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ScriptCraft comes with a couple of javascript functions that can be
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combined to build interesting things. Let's start small though to get a
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feel for how ScriptCraft's building functions work. The function you'll
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probably use most for building is called `box()` and - as its name
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implies - it is used to create cubes and cuboids of any size. A cube is
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a 3D shape whose sides are all the same length. A cuboid is a 3D shape
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whose width, height and length can differ.
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![3D Shapes][img_3d_shapes]
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You can create a Cube or a Cuboid in ScriptCraft using the `box()`
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function. You must tell the function what material you want the shape to
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be made of. For example, in the game, point the cross hairs at the
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ground, then type the following and hit enter...
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2013-12-17 22:42:25 +01:00
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/js box( blocks.oak )
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2013-12-17 22:42:25 +01:00
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... This will change the targeted block to wood. What's happened here
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is the `box()` function has created a single new wooden
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block. `blocks` is another one of those *free* variables you get in
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ScriptCraft, you can see a list of block materials by typing ...
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/js blocks.
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... then pressing the `TAB` key. Repeatedly pressing the `TAB` key
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will cycle through all of the block materials. Alternatively, you can
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see many more current materials and the numbers Minecraft uses for
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them by visiting the [Minecraft Data Values][mcdv] site.
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2013-03-23 15:14:53 +01:00
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2013-12-19 12:21:55 +01:00
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## Common Block Materials
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2013-03-23 15:14:53 +01:00
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In Minecraft Programming, Materials aren't known by their name,
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instead numbers (sometimes 2 numbers) are used to indicate which
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material should be used. For example the number 2 is grass, 1 is
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cobblestone etc, while 5 is wood (oak). There are different types of
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wood so the text '5:1' means Spruce, '5:2' means Birch and '5:3' means
|
2013-03-23 15:14:53 +01:00
|
|
|
Jungle wood. There are many different materials in the Minecraft world, the most
|
|
|
|
commonly used materials for building are:
|
|
|
|
|
2014-01-01 16:30:12 +01:00
|
|
|
* '4' - Cobblestone or `blocks.cobblestone`
|
|
|
|
* '5' - Wooden Planks or `blocks.oak`
|
|
|
|
* '5:2' - Birch wood Planks (light wood) or `blocks.birch`
|
|
|
|
* '98' - Stone bricks or `blocks.brick.stone`
|
|
|
|
* '45' - Red bricks or `blocks.brick.red`
|
|
|
|
* '68' - Sign or `blocks.sign`
|
|
|
|
* '102' - Glass panes (for windows) or `blocks.glass_pane`
|
2013-12-17 22:42:25 +01:00
|
|
|
|
|
|
|
You can create a single wooden block using the numeric values or the `blocks` variable. For example...
|
|
|
|
|
2014-01-01 16:30:12 +01:00
|
|
|
/js box( '5' )
|
2013-12-17 22:42:25 +01:00
|
|
|
|
|
|
|
... and ...
|
|
|
|
|
|
|
|
/js box( blocks.oak )
|
|
|
|
|
|
|
|
... both do exactly the same thing but I personally prefer `/js box(
|
|
|
|
blocks.oak )` because it's easier to remember. For reference, here is
|
|
|
|
a chart of all of the blocks (not items) in the Minecraft world...
|
2013-03-23 15:14:53 +01:00
|
|
|
|
|
|
|
![Minecraft Data Values][img_dv]
|
|
|
|
|
2013-12-19 12:21:55 +01:00
|
|
|
## Dimensions
|
2013-03-23 15:14:53 +01:00
|
|
|
|
|
|
|
`box()` can do more than just
|
|
|
|
create single blocks - it can create cubes and cuboids of any
|
|
|
|
size. Take a look at the following picture which shows how shapes are
|
|
|
|
measured in 3D space. There are 3 dimensions (or sizes) to consider.
|
|
|
|
|
|
|
|
1. Width
|
|
|
|
2. Height
|
|
|
|
3. Depth (or length) - not to be confused with how deep underground a
|
|
|
|
mine-shaft can go. Think of Depth (or length if you prefer) as how far
|
|
|
|
away you want something to extend.
|
|
|
|
|
|
|
|
![Width, Height and Depth][img_whd]
|
|
|
|
|
2013-12-19 12:21:55 +01:00
|
|
|
## More shapes
|
2013-03-23 15:14:53 +01:00
|
|
|
|
|
|
|
* `box0( block, width, height, depth )` - creates an empty box (with the
|
|
|
|
insides hollowed out - perfect for dwellings. `box0` will remove both
|
|
|
|
the floor and ceiling too.
|
|
|
|
* `cylinder( block, radius, height )` - creates cylinders, perfect for
|
|
|
|
Chimneys.
|
|
|
|
* `cylinder0( block, radius, height )` - creates empty cylinders -
|
|
|
|
perfect for Towers. `cylinder0` will remove both the floor and
|
|
|
|
ceiling too.
|
|
|
|
* `prism( block, width, depth )` - creates a Prism - good for roofs.
|
|
|
|
* `prism0( block, width, depth )` - creates an empty prism.
|
|
|
|
|
2013-12-19 12:21:55 +01:00
|
|
|
## The Drone Object
|
2013-03-23 15:14:53 +01:00
|
|
|
|
|
|
|
ScriptCraft is a Minecraft Mod that lets you execute Javascript code
|
|
|
|
in the game. It also lets you write your own Mod in Javacript. One
|
|
|
|
such mod that comes bundled with ScriptCraft is called the `Drone`
|
|
|
|
mod. The `Drone` is an (invsible) object you create every time you
|
|
|
|
execute any of the building or movement functions. When you execute...
|
|
|
|
|
|
|
|
/js box(5,3,2,4)
|
|
|
|
|
|
|
|
... a new `Drone` object is created and does the work of building on
|
|
|
|
your behalf. Think of a `Drone` as something like a remote control
|
|
|
|
plane that can move about freely and build things for you. Moving the
|
|
|
|
Drone is easy...
|
|
|
|
|
|
|
|
### Movement
|
|
|
|
|
|
|
|
* `up( numberOfBlocks )` - moves the Drone Up. For example: `up()`
|
|
|
|
will move the Drone 1 block up. You can tell it how many blocks to
|
|
|
|
move if you want it to move more than one block.
|
|
|
|
* `down( numberOfBlocks )` - moves the Drone Down.
|
|
|
|
* `left( numberOfBlocks )` - moves the Drone Left.
|
|
|
|
* `right( numberOfBlocs )` - moves the Drone Right.
|
|
|
|
* `fwd( numberOfBlocs )` - moves the Drone Forward (away from the player).
|
|
|
|
* `back( numberOfBlocs )` - moves the Drone Back (towards the player)
|
|
|
|
* `turn( numberOfTurns )` - Turns the Drone Clock-wise (right). For example:
|
|
|
|
`turn()` will make the Drone turn right 90 degrees. `turn(2)` will
|
|
|
|
make the Drone turn twice so that it is facing in the opposite
|
|
|
|
direction.
|
|
|
|
|
2014-01-01 16:37:01 +01:00
|
|
|
### Chaining - combining building and movement.
|
2013-03-23 15:14:53 +01:00
|
|
|
|
|
|
|
You can make a Drone move around before and after building by
|
|
|
|
*daisy-chaining* the building and movement functions together. In the
|
|
|
|
game, point at the ground then type the following...
|
|
|
|
|
2013-12-17 22:42:25 +01:00
|
|
|
/js up(1).box( blocks.oak ).fwd(3).box( blocks.oak )
|
2013-03-23 15:14:53 +01:00
|
|
|
|
|
|
|
A series of 2 boxes is created 3 blocks apart.
|
|
|
|
|
|
|
|
![Two Boxes 3 blocks apart][img_2boxes]
|
|
|
|
|
2014-01-01 16:37:01 +01:00
|
|
|
### Exercise - Build a simple dwelling
|
2013-03-23 15:14:53 +01:00
|
|
|
|
|
|
|
OK. You know enough now about the `Drone` functions to be able to
|
|
|
|
build a simple dwelling. The dwelling should be a hollow building with
|
|
|
|
a sloped roof. *Don't worry about doors or windows for now*. The walls
|
2014-01-01 16:30:12 +01:00
|
|
|
should be made of Cobblestone ('4') and the roof made of wood ('5'). You can use
|
2013-03-23 15:14:53 +01:00
|
|
|
the following `Drone` functions to create a dwelling 7 blocks wide by
|
|
|
|
3 blocks high by 6 blocks long with a wooden sloped roof. It's up
|
|
|
|
to you to figure out how.
|
|
|
|
|
|
|
|
* `up()`
|
|
|
|
* `box0()`
|
|
|
|
* `prism0()`
|
|
|
|
|
|
|
|
Your dwelling should end up looking something like this...
|
|
|
|
|
2014-01-01 16:37:01 +01:00
|
|
|
![Exercise Dwelling][img_ed]
|
2013-03-23 15:14:53 +01:00
|
|
|
|
|
|
|
### Remembering where you started.
|
|
|
|
|
|
|
|
Sometimes when you're building something big that requires lots of
|
|
|
|
manoeuvering by your Drone, you need to leave breadcrumbs as you go so
|
|
|
|
your `Drone` can return to where it started. Every new Drone has a
|
2014-01-01 16:30:12 +01:00
|
|
|
`'start'` checkpoint that it can return to by executing
|
|
|
|
`move('start')` ...
|
2013-03-23 15:14:53 +01:00
|
|
|
|
2014-01-01 16:30:12 +01:00
|
|
|
/js box('5').up(3).left(4).box('1').turn(3).fwd(5).right().box('1').move('start')
|
2013-03-23 15:14:53 +01:00
|
|
|
|
|
|
|
... A genius would have trouble figuring out how to get back
|
|
|
|
to where they started. Fortunately, they don't have to - the
|
2014-01-01 16:30:12 +01:00
|
|
|
`move('start')` function will take the Drone back to its starting
|
2013-03-23 15:14:53 +01:00
|
|
|
point.
|
|
|
|
|
|
|
|
* `chkpt( breadCrumb )` - Leaves a mark at your Drone's current
|
|
|
|
location so it can return there later. Think of it as giving a name
|
|
|
|
to the place where your Drone is located. `chkpt` is short for
|
|
|
|
Check-Point - a place in a game where you usually save your
|
|
|
|
progress.
|
|
|
|
|
|
|
|
* `move( breadCrumb )` - Moves your Drone to a location you named
|
|
|
|
using `chkpt()` . It brings your Drone back to the place where you
|
|
|
|
saved it.
|
|
|
|
|
|
|
|
Both `chkpt()` and `mark()` are useful for when you want to build
|
|
|
|
complex things that require your Drone to move about a lot ( for
|
|
|
|
example, Castles, mansions, palaces, etc).
|
|
|
|
|
2013-12-19 12:21:55 +01:00
|
|
|
## Saving your work
|
2013-03-23 15:14:53 +01:00
|
|
|
|
|
|
|
You can build cool things using the in-game command-prompt and the
|
|
|
|
`/js` command but sooner or later you'll probably want to build
|
|
|
|
something more complex and save your commands so you can run them
|
|
|
|
again when you quit the game and start it up again.
|
|
|
|
|
|
|
|
[Notepad++][np] Is a special text editor (like Notepad which comes
|
|
|
|
installed on every Windows machine) that is well suited for writing
|
|
|
|
code. If you don't already have it on your machine, you can [install
|
|
|
|
Notepad++ here][np]. I recommend using NotePad++ rather than plain old
|
2013-12-17 22:42:25 +01:00
|
|
|
Notepad because it understands Javascript. If you prefer coding on a
|
|
|
|
Macintosh, then [TextWrangler][twl] is a good programming editor which
|
|
|
|
also understands Javascript code.
|
2013-03-23 15:14:53 +01:00
|
|
|
|
2013-12-19 12:21:55 +01:00
|
|
|
## Your First Minecraft Mod!
|
2013-03-23 15:14:53 +01:00
|
|
|
|
|
|
|
So, You've learnt a little bit about Javascript and what the Drone()
|
|
|
|
object can do, let's use that knowledge to create a Minecraft Mod!
|
|
|
|
|
|
|
|
Once you've installed Notepad++, Launch it, create a new file and type the following...
|
|
|
|
|
2013-12-30 22:33:12 +01:00
|
|
|
exports.greet = function(player){
|
2014-01-01 16:30:12 +01:00
|
|
|
player.sendMessage('Hi ' + player.name);
|
2013-03-23 15:14:53 +01:00
|
|
|
}
|
|
|
|
|
|
|
|
... then save the file in a new directory
|
2014-01-02 19:46:46 +01:00
|
|
|
`craftbukkit/plugins/scriptcraft/plugins/{your_name}` (replace
|
|
|
|
{your_name} with your own name) and call the file `greet.js` (be sure
|
|
|
|
to change the file-type option to '*.* All Files' when saving or
|
|
|
|
NotePad++ will add a '.txt' extension to the filename. Now switch back
|
|
|
|
to the Minecraft game and type...
|
2013-03-23 15:14:53 +01:00
|
|
|
|
2013-12-24 23:47:57 +01:00
|
|
|
/js refresh()
|
2013-03-23 15:14:53 +01:00
|
|
|
|
2013-12-17 22:42:25 +01:00
|
|
|
... to reload all of the server plugins. Your mod has just been
|
|
|
|
loaded. Try it out by typing this command...
|
2013-03-23 15:14:53 +01:00
|
|
|
|
2014-01-01 16:30:12 +01:00
|
|
|
/js greet(self)
|
2013-03-23 15:14:53 +01:00
|
|
|
|
|
|
|
... it should display ...
|
|
|
|
|
|
|
|
Hi {your-username-here}
|
|
|
|
|
|
|
|
... where {your-username-here} will be replaced with your own
|
|
|
|
minecraft username. Congratulations - You've just written your very
|
|
|
|
first Minecraft Mod! With ScriptCraft installed, writing Minecraft
|
|
|
|
Mods is as simple as writing a new javascript function and saving it
|
2014-01-02 19:46:46 +01:00
|
|
|
in a file in the craftbukkit/plugins/scriptcraft/plugins
|
|
|
|
directory. This function will now be avaible every time you launch
|
|
|
|
minecraft. This is a deliberately trivial minecraft mod but the
|
|
|
|
principles are the same when creating more complex mods.
|
2013-12-24 23:47:57 +01:00
|
|
|
|
|
|
|
The `exports` variable is a special variable you can use in your mod
|
|
|
|
to provide functions, objects and variables for others to use. If you
|
|
|
|
want to provide something for other programmers to use, you should
|
2014-01-01 16:30:12 +01:00
|
|
|
*export* it using the special `exports` variable. The syntax is
|
2013-12-24 23:47:57 +01:00
|
|
|
straightforward and you can use the same `exports` variable to export
|
|
|
|
one or more functions, objects or variables. For example...
|
|
|
|
|
|
|
|
#### thrower.js
|
|
|
|
|
2013-12-30 22:33:12 +01:00
|
|
|
exports.egg = function(player){
|
|
|
|
player.throwEgg();
|
2013-12-24 23:47:57 +01:00
|
|
|
}
|
2013-12-30 22:33:12 +01:00
|
|
|
exports.snowball = function(player){
|
|
|
|
player.throwSnowball();
|
2013-12-24 23:47:57 +01:00
|
|
|
}
|
|
|
|
|
|
|
|
... is a plugin which provides 2 javascript functions called `egg()`
|
|
|
|
and `snowball()` which can be invoked from the in-game prompt like
|
2013-12-30 22:33:12 +01:00
|
|
|
this `/js egg(self)` or `/js snowball(self)`.
|
2013-03-23 15:14:53 +01:00
|
|
|
|
2014-01-01 16:30:12 +01:00
|
|
|
## Parameters
|
2013-03-23 15:14:53 +01:00
|
|
|
If you want to change the `greet()` function so that it displays a
|
2014-01-01 16:30:12 +01:00
|
|
|
greeting other than 'Hi ' you can change the code in the `greet()`
|
2013-03-23 15:14:53 +01:00
|
|
|
function, or better still, you can use *Parameters*. Parameters are
|
|
|
|
values you provide to a function so that the function behaves
|
|
|
|
differently each time it is called.
|
|
|
|
|
|
|
|
![greeting][img_greet]
|
|
|
|
|
|
|
|
Change the `greet()` function so that it looks like this...
|
|
|
|
|
2013-12-30 22:33:12 +01:00
|
|
|
exports.greet = function ( greeting , player) {
|
|
|
|
player.sendMessage( greeting + player.name );
|
2013-03-23 15:14:53 +01:00
|
|
|
}
|
|
|
|
|
2013-12-24 23:47:57 +01:00
|
|
|
... Save your greet.js file and issue the `/js refresh()` command in
|
2013-03-23 15:14:53 +01:00
|
|
|
minecraft. Now enter the following command in Minecraft...
|
|
|
|
|
2014-01-01 16:30:12 +01:00
|
|
|
greet('Hello ',self);
|
2013-03-23 15:14:53 +01:00
|
|
|
|
|
|
|
... Now try ...
|
|
|
|
|
2014-01-01 16:30:12 +01:00
|
|
|
greet('Dia Dhuit ',self);
|
2013-03-23 15:14:53 +01:00
|
|
|
|
|
|
|
... you should see the following messages in your chat window...
|
|
|
|
|
|
|
|
Hello {your name}
|
|
|
|
Dia Dhuit {your name}
|
|
|
|
|
|
|
|
... Parameters let you provide different values to functions each time
|
|
|
|
they're called. As you'll see later, Parameters are very useful when
|
|
|
|
changing the behaviour of MineCraft.
|
|
|
|
|
2014-01-01 16:30:12 +01:00
|
|
|
## true or false
|
2013-03-23 15:14:53 +01:00
|
|
|
|
|
|
|
Try entering each of the following statements and make a note of the
|
|
|
|
answers given by minecraft...
|
|
|
|
|
|
|
|
/js 1 < 2
|
|
|
|
|
|
|
|
/js 1 > 2
|
|
|
|
|
|
|
|
... the answer given by the first statement ( `1 < 2` ) should be
|
|
|
|
`true` since 1 is less than 2. The `<` symbol - usually found near the
|
|
|
|
bottom right of your keyboard - means test to see if something is less
|
|
|
|
than another so `1 < 2` is a way of asking the computer "is 1 less
|
|
|
|
than 2 ?". This is a silly example of course since we know 1 is less
|
|
|
|
than 2 but when dealing with variables we might not know in advance
|
|
|
|
what its value is or whether it's greater than (bigger) or less than
|
|
|
|
(smaller) another number or value. The result of the 2nd statement (`1 > 2`)
|
|
|
|
should be `false` since 1 is not greater than 2. Now try this...
|
|
|
|
|
|
|
|
/js 1 = 2
|
|
|
|
|
|
|
|
... The result won't be what you expected. You'll see an Error message
|
|
|
|
- that's OK. What's happened here is I've tried to test to see if 1 is
|
|
|
|
equal to 2 but I've made one of the most common mistakes even
|
|
|
|
experienced programmers make. If you want to test to see if two things
|
|
|
|
are the same, you use `==` that's two equals signs right next to each
|
|
|
|
other. Let's try again...
|
|
|
|
|
|
|
|
/js 1 == 2
|
|
|
|
|
|
|
|
... this time you should get an answer `false` since 1 obviously isn't
|
|
|
|
equal to 2. These are the different *operators* used when comparing
|
|
|
|
things...
|
|
|
|
|
|
|
|
* `<` Is less than ?
|
|
|
|
* `>` Is greater than ?
|
|
|
|
* `==` Is equal to ?
|
|
|
|
* `<=` Is less than or equal to ?
|
|
|
|
* `>=` Is greather than or equal to ?
|
|
|
|
* `!=` Is not equal to ?
|
|
|
|
|
|
|
|
... try comparing some more numbers yourself - say for example,
|
|
|
|
compare the ages of your friends or siblings to your own age.
|
|
|
|
|
2014-01-01 16:30:12 +01:00
|
|
|
## More fun with `true` or `false`
|
2013-03-23 15:14:53 +01:00
|
|
|
You can find out if you can Fly in minecraft by typing the following statement...
|
|
|
|
|
|
|
|
/js self.allowFlight
|
|
|
|
|
|
|
|
... the result will be `true` or `false` depending on whether you can
|
|
|
|
fly or not. You can turn on and off your ability to fly by setting
|
|
|
|
your `allowFlight` property to `true` or `false`. Try it...
|
|
|
|
|
|
|
|
/js self.allowFlight = true
|
|
|
|
|
|
|
|
... Now you can fly! To turn off flight...
|
|
|
|
|
|
|
|
/js self.allowFlight = false
|
|
|
|
|
|
|
|
... and you come crashing down to earth. This is just one example of
|
|
|
|
how `true` and `false` are used throughout ScriptCraft - these are
|
|
|
|
called `boolean` values - named after [George Boole][boole], a 19th Century
|
|
|
|
Maths Professor at University College Cork. There are plenty more
|
|
|
|
examples of boolean values in Minecraft. You can find out if monsters
|
|
|
|
are allowed in your minecraft world by typing the following
|
|
|
|
statement...
|
|
|
|
|
|
|
|
/js self.location.world.allowMonsters
|
|
|
|
|
|
|
|
... The result of this statement will be either `false` (Phew!) or
|
|
|
|
`true` (Yikes!) depending on how your server has been
|
|
|
|
configured. However, typing the following statement doesn't work as
|
|
|
|
expected...
|
|
|
|
|
|
|
|
/js self.location.world.allowMonsters = true
|
|
|
|
|
|
|
|
... This statement won't work as expected - it will give an Error
|
|
|
|
message. This is because sometimes we can read variables but we can't
|
|
|
|
change them the same way we read them (this is because of how
|
|
|
|
Javascript, Java and the CraftBukkit API work together). To turn on or
|
|
|
|
off the spawning of monsters, type the following...
|
|
|
|
|
|
|
|
/js self.location.world.setSpawnFlags(false, true)
|
|
|
|
|
|
|
|
... the `setSpawnFlags()` method takes 2 parameters, the first
|
|
|
|
parameter says whether or not monsters can spawn, and the 2nd says
|
|
|
|
whether or not Animals can spawn. (SIDENOTE: You may be wondering how
|
|
|
|
to change other aspects of the Minecraft game - pretty much all
|
|
|
|
aspects of the game can be changed. Changes are made using what are
|
|
|
|
called `API` calls - these are calls to functions and methods in
|
|
|
|
Minecraft - you can read more about these on the [CraftBukkit API
|
|
|
|
Reference][cbapi].)
|
|
|
|
|
2014-01-01 16:30:12 +01:00
|
|
|
## ...and Again, and Again, and Again,...
|
2013-03-23 15:14:53 +01:00
|
|
|
|
|
|
|
One of the things Computers are really good at is
|
|
|
|
repetition. Computers don't get tired or bored of doing the same thing
|
|
|
|
over and over again. Loops are handy, if you want to run the same
|
|
|
|
code over and over again, each time with a different value.
|
|
|
|
|
2014-01-01 16:30:12 +01:00
|
|
|
### Counting to 100
|
2013-03-23 15:14:53 +01:00
|
|
|
|
|
|
|
At the in-game command prompt (hint: press 't') type the following then hit Enter...
|
|
|
|
|
|
|
|
/js for (var i = 1 ; i <= 100 ; i = i + 1) { echo( i ); }
|
|
|
|
|
|
|
|
... The above code will count from 1 to 100. The first thing you'll
|
|
|
|
notice if you run the above code is how quickly the count
|
|
|
|
happened. You're probably curious how long it would take to count to
|
|
|
|
1000. Try it out for yourself. Change the above line of code so that
|
|
|
|
it counts to 1000 instead of 100. If you're feeling adventurous, see
|
|
|
|
how long it takes to count to ten thousand, one hundred thousand or even one million.
|
|
|
|
|
|
|
|
The `for` statement is useful when you want to repeat something over and over. It has 4 parts...
|
|
|
|
|
|
|
|
1. The initialiser: `var i = 1` - this happens once at the start of the loop.
|
|
|
|
2. The test: `i <= 100` - this happens at the start of each run around the loop. If the test fails, then the loop ends.
|
|
|
|
3. The increment: `i = i + 1` - this happens at the end of each run
|
|
|
|
around the loop. If you didn't have a statement here, the loop might
|
|
|
|
never finish. `i = i + 1` is often written as `i++` - it's shorter
|
|
|
|
and does basically the same thing.
|
|
|
|
4. The body - everything that appears between the `{` and `}` (opening and closing curly braces).
|
|
|
|
|
|
|
|
|
|
|
|
`for` loops becomes very useful when you combine it with Arrays -
|
|
|
|
remember, an Array is just a list of things, for example - the players
|
|
|
|
connnected to a server, the worlds of a server and so on.
|
|
|
|
|
2014-01-01 16:30:12 +01:00
|
|
|
### Saying "Hi!" to every player
|
2013-03-23 15:14:53 +01:00
|
|
|
|
|
|
|
At the in-game command prompt type the following then hit Enter...
|
|
|
|
|
2014-01-01 16:30:12 +01:00
|
|
|
/js for (var i = 0;i < server.onlinePlayers.length; i++){ server.onlinePlayers[i].sendMessage('Hi!'); }
|
2013-03-23 15:14:53 +01:00
|
|
|
|
|
|
|
... Lets look at these statements in more detail. We had to enter the
|
|
|
|
statements on a single line at the in-game command prompt but the
|
|
|
|
statements could be written like this...
|
|
|
|
|
|
|
|
var players = server.onlinePlayers;
|
|
|
|
for (var i = 0; i < players.length; i++) {
|
|
|
|
var player = players[i];
|
2014-01-01 16:30:12 +01:00
|
|
|
player.sendMessage('Hi!');
|
2013-03-23 15:14:53 +01:00
|
|
|
}
|
|
|
|
|
|
|
|
... On the first line, a new variable `players` is created from the
|
|
|
|
server object's onlinePlayers property. `players` is more concise and
|
|
|
|
easier to type than the long-winded `server.onlinePlayers`. On the
|
|
|
|
second line, the for loop is declared, a counter variable `i` is set
|
|
|
|
to 0 (zero - arrays in javascript start at 0 not 1) and each time
|
|
|
|
around the loop is tested to see if it's less than the number of
|
|
|
|
players online. At the end of each run around the loop the `i`
|
|
|
|
variable is incremented (increased by 1) so that the next player can
|
|
|
|
be messaged. Inside the body of the for loop (everything between the
|
|
|
|
opening `{` and closing `}` curly braces) the `players[i]` expression
|
|
|
|
refers to the player in the players array at position[i]. Imagine
|
|
|
|
there are 4 players online on a minecraft server, the `players` array
|
|
|
|
might look like this...
|
|
|
|
|
|
|
|
* players[0] = 'CrafterJohn'
|
|
|
|
* players[1] = 'MinerPaul'
|
|
|
|
* players[2] = 'ExplorerRingo'
|
|
|
|
* players[3] = 'TraderGeorge'
|
|
|
|
|
|
|
|
... in this case `players.length` will be 4 (since there are 4 online
|
|
|
|
players), the for-loop will go around 4 times starting from position 0
|
|
|
|
and going all the way up to position 3, sending a message to each of
|
|
|
|
the players in the array. It's time for a new scriptcraft
|
|
|
|
function. Open the `hi.js` file you created earlier (using NotePad++ ,
|
|
|
|
TextWrangler or your editor of choice) and add the following code at
|
|
|
|
the bottom of the file...
|
|
|
|
|
2013-12-24 23:47:57 +01:00
|
|
|
exports.hiAll = function (){
|
2013-03-23 15:14:53 +01:00
|
|
|
var players = server.onlinePlayers;
|
|
|
|
for (var i = 0; i < players.length; i++) {
|
|
|
|
var player = players[i];
|
2014-01-01 16:30:12 +01:00
|
|
|
player.sendMessage('Hi!');
|
2013-03-23 15:14:53 +01:00
|
|
|
}
|
|
|
|
}
|
|
|
|
|
|
|
|
... save the file, at the in-game command prompt type `reload` and
|
|
|
|
then type `/js hiAll()`. This will send the message `Hi!` to all of
|
|
|
|
the players connected to your server. You've done this using a `for`
|
|
|
|
loop and arrays. Arrays and `for` loops are used heavily in all types
|
|
|
|
of software, in fact there probably isn't any software that doesn't
|
|
|
|
use `for` loops and Arrays to get things done.
|
|
|
|
|
2014-01-01 16:30:12 +01:00
|
|
|
## While Loops
|
2013-03-23 15:14:53 +01:00
|
|
|
|
|
|
|
Another way to repeat things over and over is to use a `while`
|
|
|
|
loop. The following `while` loop counts to 100...
|
|
|
|
|
|
|
|
var i = 1;
|
|
|
|
while (i <= 100){
|
2013-12-30 22:33:12 +01:00
|
|
|
console.log( i );
|
2013-03-23 15:14:53 +01:00
|
|
|
i = i + 1;
|
|
|
|
}
|
|
|
|
|
|
|
|
A `while` loop will repeat until its condition is `false` - the
|
|
|
|
condition in the above example is `i <= 100` so while i is less than
|
|
|
|
or equal to 100 the code within the `while` block (everything between
|
|
|
|
the starting `{` and ending `}` curly braces) will run. It's important
|
|
|
|
that you change the variable being tested in a while loop, otherwise
|
|
|
|
the while loop will never it - it will run forever. Try running the
|
|
|
|
following code...
|
|
|
|
|
|
|
|
/js var i = 1; while (i <= 100){ echo( i ); }
|
|
|
|
|
|
|
|
The code above will contine printing out the number 1 until the end of
|
|
|
|
time (or until you unplug your computer). That's because the `i`
|
|
|
|
variable is never incremented (remember - incrementing just means
|
|
|
|
adding 1 to it) so i will always be 1 and never changes meaning the
|
|
|
|
loop goes on forever. Again - this is a mistake even experienced programmers sometimes make.
|
|
|
|
|
|
|
|
Just like `for` loops, `while` loops can be also be used to loop
|
|
|
|
through arrays. The following loop prints out all of the players on
|
|
|
|
the server...
|
|
|
|
|
|
|
|
var players = server.onlinePlayers;
|
|
|
|
var i = 0;
|
|
|
|
while ( i < players.length ) {
|
2013-12-30 22:33:12 +01:00
|
|
|
console.log( players[i] );
|
2013-03-23 15:14:53 +01:00
|
|
|
i = i + 1;
|
|
|
|
}
|
|
|
|
|
|
|
|
... whether you chose to use a `for` loop or a `while` loop is largely
|
|
|
|
a matter of personal taste, `for` loops are more commonly used with
|
|
|
|
Arrays but as you see from the example above, `while` loops can also
|
|
|
|
loop over Arrays.
|
|
|
|
|
2014-01-01 16:30:12 +01:00
|
|
|
## `utils.foreach()` - Yet another way to process Arrays
|
2013-03-23 15:14:53 +01:00
|
|
|
|
|
|
|
Both the `for` statement and `while` statement are standard commonly
|
|
|
|
used javascript statements used for looping. ScriptCraft also comes
|
|
|
|
with a special function for looping called `utils.foreach()`.
|
|
|
|
utils.foreach() is a convenience function, you don't have to use it if
|
|
|
|
you prefer the syntax of javascript's `for` and `while`
|
|
|
|
loops. utils.foreach() takes two parameters...
|
|
|
|
|
|
|
|
1. An array
|
|
|
|
2. A function which will be called for each item in the array.
|
|
|
|
|
|
|
|
...that's right, you can pass functions as parameters in javascript!
|
2013-12-30 22:33:12 +01:00
|
|
|
Let's see it in action, the following code will `console.log()` (print) the
|
|
|
|
name of each online player in the server console window...
|
2013-03-23 15:14:53 +01:00
|
|
|
|
2013-12-30 22:33:12 +01:00
|
|
|
utils.foreach( server.onlinePlayers, console.log );
|
2013-03-23 15:14:53 +01:00
|
|
|
|
|
|
|
... in the above example, the list of online players is processed one
|
2013-12-30 22:33:12 +01:00
|
|
|
at a time and each item (player) is passed to the `console.log`
|
|
|
|
function. Note here that I used `console.log` not `console.log()`. The round braces
|
2013-03-23 15:14:53 +01:00
|
|
|
() are used to call the function. If I want to pass the function as a
|
|
|
|
parameter, I just use the function name without the round braces. The
|
2013-12-30 22:33:12 +01:00
|
|
|
above example uses a named function which already exists ( `console.log` ),
|
2013-03-23 15:14:53 +01:00
|
|
|
you can also create new functions on-the-fly and pass them to the
|
|
|
|
utils.foreach() function...
|
|
|
|
|
|
|
|
/*
|
|
|
|
give every player the ability to fly.
|
|
|
|
*/
|
2013-12-24 23:47:57 +01:00
|
|
|
var utils = require('utils');
|
2013-03-23 15:14:53 +01:00
|
|
|
utils.foreach( server.onlinePlayers,
|
|
|
|
function (player) {
|
|
|
|
player.setAllowFlight(true);
|
|
|
|
}
|
|
|
|
);
|
|
|
|
|
2013-03-23 16:56:15 +01:00
|
|
|
... Another example, this time each player will hear a Cat's Meow...
|
|
|
|
|
|
|
|
/*
|
|
|
|
Play a Cat's Meow sound for each player.
|
|
|
|
*/
|
2013-12-24 23:47:57 +01:00
|
|
|
var utils = require('utils');
|
2013-03-23 16:56:15 +01:00
|
|
|
utils.foreach( server.onlinePlayers,
|
|
|
|
function (player) {
|
|
|
|
player.playSound(player.location,
|
|
|
|
org.bukkit.Sound.CAT_MEOW,
|
|
|
|
1,
|
|
|
|
1);
|
|
|
|
|
|
|
|
}
|
|
|
|
);
|
|
|
|
|
2014-01-01 16:30:12 +01:00
|
|
|
### Exercise
|
2013-04-13 14:22:38 +02:00
|
|
|
Try changing the above function so that different sounds are played
|
|
|
|
instead of a Cat's Meow. You'll need to lookup the [CraftBukkit API's
|
|
|
|
Sound class][soundapi] to see all of the possible sounds that can be
|
|
|
|
played.
|
2013-03-23 16:56:15 +01:00
|
|
|
|
2013-03-23 15:14:53 +01:00
|
|
|
Loops are a key part of programming in any language. Javascript
|
|
|
|
provides `for` and `while` statements for looping and many javascript
|
|
|
|
libraries also provide their own custom looping functions. You should
|
|
|
|
use what you feel most comfortable with.
|
|
|
|
|
2014-01-01 16:30:12 +01:00
|
|
|
## Putting `for` loops to use - Building a Skyscraper
|
2013-04-13 14:22:38 +02:00
|
|
|
|
|
|
|
For loops can be used to build enormous structures. In this next
|
|
|
|
exercise I'm going to use a for loop to build a skyscraper. This
|
|
|
|
skyscraper will be made of Glass and Steel (just like most skyscrapers
|
|
|
|
in real-life). The first thing to do is see what a single floor of
|
|
|
|
the skyscraper will look like. Place a block (of any type) where you
|
|
|
|
want to eventually build the skyscraper, then while your cursor is
|
|
|
|
pointing at the block, type the following into the in-game prompt...
|
|
|
|
|
|
|
|
/js var drone = box(blocks.iron,20,1,20).up().box0(blocks.glass_pane,20,3,20).up(3)
|
|
|
|
|
|
|
|
... you should a large (20x20) iron floor with 3 block high glass all around.
|
|
|
|
|
|
|
|
![skyscraper-floor.png][img_ssf]
|
|
|
|
|
|
|
|
... A skyscraper with just a single floor isn't much of a skyscraper
|
|
|
|
so the next step is to repeat this over and over. This is where `for`
|
|
|
|
loops come in. Open your favorite text editor and create a new file in
|
2013-12-24 23:47:57 +01:00
|
|
|
your scriptcraft/plugins/{your-name} directory, name the file `myskyscraper.js`, then
|
2013-04-13 14:22:38 +02:00
|
|
|
type the following...
|
|
|
|
|
2014-01-04 23:06:23 +01:00
|
|
|
var myskyscraper = function(floors) {
|
|
|
|
if (typeof floors == 'undefined'){
|
|
|
|
floors = 10;
|
|
|
|
}
|
2013-12-24 23:47:57 +01:00
|
|
|
this.chkpt('myskyscraper'); // saves the drone position so it can return there later
|
2013-04-13 14:22:38 +02:00
|
|
|
for (var i = 0; i < floors; i++)
|
|
|
|
{
|
2014-01-04 23:06:23 +01:00
|
|
|
this.box(blocks.iron,20,1,20)
|
|
|
|
.up()
|
|
|
|
.box0(blocks.glass_pane,20,3,20)
|
|
|
|
.up(3);
|
2013-04-13 14:22:38 +02:00
|
|
|
}
|
2013-12-24 23:47:57 +01:00
|
|
|
return this.move('myskyscraper'); // return to where we started
|
2013-04-13 14:22:38 +02:00
|
|
|
};
|
|
|
|
|
2014-01-04 23:06:23 +01:00
|
|
|
var Drone = require('../drone/drone.js').Drone;
|
2013-12-24 23:47:57 +01:00
|
|
|
Drone.extend('myskyscraper',myskyscraper);
|
2013-04-13 14:22:38 +02:00
|
|
|
|
|
|
|
... so this takes a little explaining. First I create a new function
|
2013-12-24 23:47:57 +01:00
|
|
|
called myskyscraper that will take a single parameter `floors` so that
|
|
|
|
when you eventually call the `myskyscraper()` function you can tell it
|
2013-04-13 14:22:38 +02:00
|
|
|
how many floors you want built. The first statement in the function
|
2014-01-04 23:06:23 +01:00
|
|
|
`if (typeof floors == 'undefined'){ floors = 10; }` sets floors to 10 if no parameter is
|
|
|
|
supplied. The next statement `this.chkpt('myskyscraper')` saves
|
2013-04-13 14:22:38 +02:00
|
|
|
the position of the Drone so it can eventually return to where it
|
|
|
|
started when finished building (I don't want the drone stranded atop
|
|
|
|
the skyscraper when it's finished). Then comes the `for` loop. I loop
|
|
|
|
from 0 to `floors` and each time through the loop I build a single
|
|
|
|
floor. When the loop is done I return the drone to where it started.
|
|
|
|
The last 2 lines load the drone module (it must be loaded before I can
|
|
|
|
add new features to it) and the last line extends the 'Drone' object
|
|
|
|
so that now it can build skyscrapers among other things. Once you've
|
|
|
|
typed in the above code and saved the file, type `reload` in your
|
|
|
|
in-game prompt, then type ...
|
|
|
|
|
2013-12-24 23:47:57 +01:00
|
|
|
/js myskyscraper(2);
|
2013-04-13 14:22:38 +02:00
|
|
|
|
|
|
|
... A two-story skyscraper should appear. If you're feeling
|
|
|
|
adventurous, try a 10 story skyscraper! Or a 20 story skyscraper!
|
|
|
|
Minecraft has a height limit (256 blocks from bedrock) beyond which
|
|
|
|
you can't build. If you try to build higher than this then building
|
|
|
|
will stop at that height.
|
|
|
|
|
|
|
|
![skyscraper][img_ss]
|
|
|
|
|
2013-04-14 16:20:02 +02:00
|
|
|
I'll leave it as an exercise to the reader to create a city block of
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skyscrapers, 5 blocks apart using a for loop. Once you've figured
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that out, creating an entire city of blocks of skyscrapers is the next
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logical step. Of course, Minecraft doesn't have the same constraints
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as real-world densely populated areas so let your imagination go wild.
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2014-01-01 16:30:12 +01:00
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## Making Decisions
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2013-05-04 18:31:13 +02:00
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All the programs we have seen so far have been fairly predictable - they went
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straight through the statements, and then went back to the beginning again. This is
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not very useful. In practice the computer would be expected to make decisions and
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act accordingly. The javascript statement used for making decisions is `if`.
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While standing on the ground in-game, type the following at the command prompt...
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2014-01-01 16:30:12 +01:00
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/js if ( self.flying ) { echo('Hey, You are flying!'); }
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2013-05-04 18:31:13 +02:00
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... No message should appear on screen. That is - `Hey, You are
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flying!` should *not* appear on screen. Now double-tap the `space`
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bar to start flying in-game (tap the space bar twice in rapid
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succession), then press and hold space to rise above the ground. Now
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enter the same statement again (If you don't want to type the same
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statement again, just press `/` then press the `UP` cursor key on your
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keyboard, the statement you entered previously should reappear.
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2014-01-01 16:30:12 +01:00
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/js if ( self.flying ) { echo('Hey, You are flying!'); }
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2013-05-04 18:31:13 +02:00
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... this time the following message should have appeared on your screen...
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Hey, You are flying!
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The `if` statement tests to see if something is `true` or `false` and
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if `true` then the block of code between the curly braces ( `{` and
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`}` ) is executed - but only if the condition is true. The condition
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in the above example is `self.flying` which will be `true` if you are
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currently flying or `false` if you aren't.
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What if you wanted to display a message only if a condition is *not*
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true ? For example to only display a message if the player is *not*
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flying...
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2014-01-01 16:30:12 +01:00
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/js if ( ! self.flying ) { echo ('You are not flying.'); }
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2013-05-04 18:31:13 +02:00
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... This code differs in that now there's a `!` (the exclamation mark)
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before `self.flying`. The `!` symbol negates (returns the opposite of)
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whatever follows it.
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What if you want to display a message in both cases - whether you're
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flying or not? This is where the `if - else` construct comes in handy.
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Open your favorite editor and type the following code into a new file
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2013-12-24 23:47:57 +01:00
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in your scriptcraft/plugins directory...
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2013-05-04 18:31:13 +02:00
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2013-12-30 22:33:12 +01:00
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function flightStatus(player)
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2013-05-04 18:31:13 +02:00
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{
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2013-12-30 22:33:12 +01:00
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if ( player.flying )
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2013-05-04 18:31:13 +02:00
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{
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2013-12-30 22:33:12 +01:00
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player.sendMessage( 'Hey, You are flying!' );
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2013-05-04 18:31:13 +02:00
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}
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else
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{
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2013-12-30 22:33:12 +01:00
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player.sendMessage( 'You are not flying.' );
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2013-05-04 18:31:13 +02:00
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}
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}
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