Working with HTML, CSS, and JavaScript

Hypertext Markup Language (HTML) is a language for specifying the layout of web pages. It is a markup language that defines the structure of your content declaratively, which makes it very powerful. Ember provides a templating language that extends HTML and provides tools for making that structure dynamic.

If you're new to HTML, we recommend Mozilla's HTML Tutorial is fairly comprehensive, and the MDN site is one of the best resources for learning about web APIs.

CSS (Cascading Style Sheets) are used to style HTML. While HTML lays out the basic structure, CSS provides the rules for how that structure should display in the browser.

If you're new to CSS, we recommend the MDN guide for learning it, as it is fairly comprehensive and up to date.

JavaScript is the primary scripting language of the web. Most Ember apps have some amount of JavaScript code in them.

Since Ember is a template-oriented framework, not all developers need to use JavaScript when working on Ember apps. Some developers may be more focused on the structure of an app's templates, its styles, or the accessibility an app. However, it's good to have some general knowledge of JavaScript for the places where it is used.

If you're new to JavaScript, here are some excellent introductory materials:

• Mozilla's JavaScript Tutorial is pretty comprehensive, and the MDN documentation is the go-to source for learning about JavaScript and web APIs.
• javascript.info is a detailed interactive guide that takes you through from the basics to the details. This one is pretty good for beginners with no programming experience, since it starts from scratch and ramps up.
• ES6 for humans is a great resource if you're already familiar with JavaScript in general, but haven't had a chance to get to know some of its latest features that were finalized in 2015.

We recommend familiarizing yourself with the following concepts in particular to make the most out of these guides and of Ember:

• Classes - classes are one of the most fundamental constructs in JavaScript, and are used frequently in Ember. See the next section for more details on them.
• Modules - you will better understand Ember CLI's project structure and import paths if you are comfortable with JavaScript Modules.
• Events - The native way to deal with user input in browser based web applications. Events are not part of the language of JavaScript itself, but they are part of the browser environment that JavaScript runs in, and they are used commonly in Ember. You can read the MDN introduction to events for more details.
• Promises - the native way to deal with asynchrony in your JavaScript code. See the relevant Mozilla Developer Network section. In addition, modern async/await function syntax is good to know.

Ember uses JavaScript classes for many of its constructs, such as Components, Routes, Services, and more:

export default class PermissionController extends Controller {
  @tracked isAdmin = false;
  @tracked isManager = false;

  get canEdit() {
    return this.isAdmin || this.isManager;
  }
}

Some of the features that Ember relies on, such as class fields and decorators have not yet been fully finalized in JavaScript just yet, so we'll cover these here with the assumption that you've had a chance to familiarize yourself with classes before. If you haven't, you can also check out our detailed class primer.

Class fields allow you to assign properties to an instance of the class on construction. You can define a field like this:

class Permission {
  canEdit = false;
}

This is very similar to defining the Permission class with a constructor like this:

class Permission {
  constructor() {
    this.canEdit = false;
  }
}

Class fields are somewhat like object properties, but they have some key differences. They are created and assigned to every instance of the class, meaning that instance gets a unique version of the field. This doesn't matter if the field is a primitive, like a string or a number, but does matter if it's an object or an array:

class Permission {
  roles = [];
}

let tom = new Permission();
let yehuda = new Permission();

tom.roles === yehuda.roles;
// false, they're different arrays

Fields can also access the class instance using this when they are being assigned:

class Child {
  constructor(parent) {
    this.parent = parent;
  }
}

class Parent {
  child = new Child(this);
}

Fields are assigned before any code in the constructor method is run, which is why we can rely on them being assigned correctly by the time it runs. Fields do not exist on the class itself, nor do they exist on the class's prototype, they only exist on the instance of the class. However, they can be added to the class directly using the static keyword, like other class elements.

Decorators are user defined modifiers that can be applied to a class or class element such as a field or method to change its behavior. For instance, you could create a @cache decorator that caches the return value of a getter the first time it is calculated:

import { cache } from 'my-cache-decorator';

class Counter {
  _count = 0;

  @cache
  get count() {
    return this._count++;
  }
}

let counter = new Counter();

console.log(counter.count); // 0
console.log(counter.count); // 0

Decorators are normal JavaScript functions that get applied with a special syntax, which is why you import them like any other function, but you use the @ symbol when applying them. Decorators come in a variety of flavors, and some can be applied to classes directly as well:

@observable
class Permission {}

Some decorators can also receive arguments:

class Permission {
  canEdit = false;

  @alias('canEdit') editable;
}

let current = new Permission();
console.log(current.editable); // false

Ember provides a number of decorators, such as the @tracked decorator, that will be described in greater detail later on in the guides.

Note: Decorators are still being actively developed in JavaScript, which means that there may be small changes in the future. The decorators provided by Ember should remain stable through these changes, but it is recommended that you exercise caution if using any external decorator libraries which may not have the same stability guarantees.

Ember used its own custom class syntax before native JavaScript classes existed, which looks like this:

export default Controller.extend({
  isAdmin: tracked({ value: false }),
  isManager: tracked({ value: false }),

  canEdit: descriptor({
    get() {
      return this.isAdmin || this.isManager;
    },
  }),
});

This syntax is known as classic class syntax, and if you're starting out on a new Ember application it's recommended that you stick with native classes instead. However, if you are working in an older application, or in an addon, you may encounter this syntax, so you can check out the pre-Octane guides on classic classes for more information on them.

Just like the JavaScript language changes over time, web browsers change too! Ember helps you to write code that can work across many different browsers and their versions. Behind the scenes, Ember uses Babel to compile modern JavaScript to something that can work on all browsers. Without this step, you could accidentally end up shipping code that works for your version of Chrome but breaks for someone using Edge. Ember has you covered!

Luckily, Ember comes with a solution out of the box for this. Ember applications use Babel to compile modern JavaScript to something that can work on all browsers. This means you can write modern JavaScript and use the latest features without any additional setup!

Note: Some features require you to enable the Babel polyfill. This adds some extra weight to your application, but ensures you'll be compatible with any new features that are added to JavaScript.