Prerequisites
These articles are meant to help you learn how to use three.js.
They assume you know how to program in JavaScript. They assume
you know what the DOM is, how to write HTML as well as create DOM elements
in JavaScript. They assume you know how to use
es6 modules
via import and via <script type="module"> tags. They assume you know how to use import maps.
They assume you know some CSS and that you know what
CSS selectors are.
They also assume you know ES5, ES6 and maybe some ES7.
They assume you know that the browser runs JavaScript only via events and callbacks.
They assume you know what a closure is.
Here's some brief refreshers and notes
es6 modules
es6 modules can be loaded via the import keyword in a script
or inline via a <script type="module"> tag. Here's an example
<script type="importmap">
{
"imports": {
"three": "./path/to/three.module.js",
"three/addons/": "./different/path/to/examples/jsm/"
}
}
</script>
<script type="module">
import * as THREE from 'three';
import {OrbitControls} from 'three/addons/controls/OrbitControls.js';
...
</script>
See more details at the bottom of this article.
document.querySelector and document.querySelectorAll
You can use document.querySelector to select the first element
that matches a CSS selector. document.querySelectorAll returns
all elements that match a CSS selector.
You don't need onload
Lots of 20yr old pages use HTML like
<body onload="somefunction()">
That style is deprecated. Put your scripts at the bottom of the page.
<html>
<head>
...
</head>
<body>
...
</body>
<script>
// inline javascript
</script>
</html>
Know how closures work
function a(v) {
const foo = v;
return function() {
return foo;
};
}
const f = a(123);
const g = a(456);
console.log(f()); // prints 123
console.log(g()); // prints 456
In the code above the function a creates a new function every time it's called. That
function closes over the variable foo. Here's more info.
Understand how this works
this is not magic. It's effectively a variable that is automatically passed to functions just like
an argument is passed to function. The simple explanation is when you call a function directly
like
somefunction(a, b, c);
this will be null (when in strict mode or in a module) where as when you call a function via the dot operator . like this
someobject.somefunction(a, b, c);
this will be set to someobject.
The parts where people get confused is with callbacks.
const callback = someobject.somefunction; loader.load(callback);
doesn't work as someone inexperienced might expect because when
loader.load calls the callback it's not calling it with the dot . operator
so by default this will be null (unless the loader explicitly sets it to something).
If you want this to be someobject when the callback happens you need to
tell JavaScript that by binding it to the function.
const callback = someobject.somefunction.bind(someobject); loader.load(callback);
this article might help explain this.
ES5/ES6/ES7 stuff
var is deprecated. Use const and/or let
There is no reason to use var EVER and at this point it's considered bad practice
to use it at all. Use const if the variable will never be reassigned which is most of
the time. Use let in those cases where the value changes. This will help avoid tons of bugs.
Use for(elem of collection) never for(elem in collection)
for of is new, for in is old. for in had issues that are solved by for of
As one example you can iterate over all the key/value pairs of an object with
for (const [key, value] of Object.entries(someObject)) {
console.log(key, value);
}
Use forEach, map, and filter where useful
Arrays added the functions forEach,
map, and
filter and
are used fairly extensively in modern JavaScript.
Use destructuring
Assume an object const dims = {width: 300, height: 150}
old code
const width = dims.width; const height = dims.height;
new code
const {width, height} = dims;
Destructuring works with arrays too. Assume an array const position = [5, 6, 7, 1];
old code
const y = position[1]; const z = position[2];
new code
const [, y, z] = position;
Destructuring also works in function arguments
const dims = {width: 300, height: 150};
const vector = [3, 4];
function lengthOfVector([x, y]) {
return Math.sqrt(x * x + y * y);
}
const dist = lengthOfVector(vector); // dist = 5
function area({width, height}) {
return width * height;
}
const a = area(dims); // a = 45000
Use object declaration short cuts
old code
const width = 300;
const height = 150;
const obj = {
width: width,
height: height,
area: function() {
return this.width * this.height
},
};
new code
const width = 300;
const height = 150;
const obj = {
width,
height,
area() {
return this.width * this.height;
},
};
Use the rest parameter and the spread operator ...
The rest parameter can be used to consume any number of parameters. Example
function log(className, ...args) {
const elem = document.createElement('div');
elem.className = className;
elem.textContent = args.join(' ');
document.body.appendChild(elem);
}
The spread operator can be used to expand an iterable into arguments
const position = [1, 2, 3]; someMesh.position.set(...position);
or copy an array
const copiedPositionArray = [...position]; copiedPositionArray.push(4); // [1,2,3,4] console.log(position); // [1,2,3] position is unaffected
or to merge objects
const a = {abc: 123};
const b = {def: 456};
const c = {...a, ...b}; // c is now {abc: 123, def: 456}
Use class
The syntax for making class like objects pre ES5 was unfamiliar to most
programmers. As of ES5 you can now use the class
keyword
which is closer to the style of C++/C#/Java.
Understand getters and setters
Getters and
setters are
common in most modern languages. The class syntax
of ES5 makes them much easier than pre ES5.
Use arrow functions where appropriate
This is especially useful with callbacks and promises.
loader.load((texture) => {
// use texture
});
Arrow functions bind this to the context in which you create the arrow function.
const foo = (args) => {/* code */};
is a shortcut for
const foo = (function(args) {/* code */}).bind(this));
See link above for more info on this.
Promises as well as async/await
Promises help with asynchronous code. Async/await help use promises.
It's too big a topic to go into here but you can read up on promises here and async/await here.
Use Template Literals
Template literals are strings using backticks instead of quotes.
const foo = `this is a template literal`;
Template literals have basically 2 features. One is they can be multi-line
const foo = `this is a template literal`; const bar = "this\nis\na\ntemplate\nliteral";
foo and bar above are the same.
The other is that you can pop out of string mode and insert snippets of
JavaScript using ${javascript-expression}. This is the template part. Example:
const r = 192;
const g = 255;
const b = 64;
const rgbCSSColor = `rgb(${r},${g},${b})`;
or
const color = [192, 255, 64];
const rgbCSSColor = `rgb(${color.join(',')})`;
or
const aWidth = 10;
const bWidth = 20;
someElement.style.width = `${aWidth + bWidth}px`;
Learn JavaScript coding conventions.
While you're welcome to format your code any way you chose there is at least one convention you should be aware of. Variables, function names, method names, in JavaScript are all lowerCasedCamelCase. Constructors, the names of classes are CapitalizedCamelCase. If you follow this rule your code will match most other JavaScript. Many linters, programs that check for obvious errors in your code, will point out errors if you use the wrong case since by following the convention above they can know when you're using something incorrectly.
const v = new vector(); // clearly an error if all classes start with a capital letter const v = Vector(); // clearly an error if all functions start with a lowercase letter.
Consider using Visual Studio Code
Of course use whatever editor you want but if you haven't tried it consider using Visual Studio Code for JavaScript and after installing it setup eslint. It might take a few minutes to setup but it will help you immensely with finding bugs in your JavaScript.
Some examples
If you enable the no-undef rule then
VSCode via ESLint will warn you of many undefined variables.
Above you can see I mis-spelled doTheThing as doThing. There's a red squiggle
under doThing and hovering over it it tells me it's undefined. One error
avoided.
If you're using <script> tags to include three.js you'll get warnings using THREE so add /* global THREE */ at the top of your
JavaScript files to tell eslint that THREE exists. (or better, use import 😉)
Above you can see eslint knows the rule that UpperCaseNames are constructors
and so you should be using new. Another error caught and avoided. This is the
new-cap rule.
There are 100s of rules you can turn on or off or
customize. For example above I mentioned you
should use const and let over var.
Here I used var and it warned me I should use let or const
Here I used let but it saw I never change the value so it suggested I use const.
Of course if you'd prefer to keep using var you can just turn off that rule.
As I said above though I prefer to use const and let over var as they just
work better and prevent bugs.
For those cases where you really need to override a rule you can add comments to disable them for a single line or a section of code.
If you really need to support legacy browsers use a transpiler
Most modern browsers are auto-updated so using all these features will help you be productive and avoid bugs. That said, if you're on a project that absolutely must support old browsers there are tools that will take your ES5/ES6/ES7 code and transpile the code back to pre ES5 Javascript.