Airbnb JavaScript Style Guide() {

A mostly reasonable approach to JavaScript


For the ES5-only guide click here.

1. Types
2. References
3. Objects
4. Arrays
5. Destructuring
6. Strings
7. Functions
8. Arrow Functions
9. Constructors
10. Modules
11. Iterators and Generators
12. Properties
13. Variables
14. Hoisting
15. Comparison Operators & Equality
16. Blocks
17. Comments
18. Whitespace
19. Commas
20. Semicolons
21. Type Casting & Coercion
22. Naming Conventions
23. Accessors
24. Events
25. jQuery
26. ECMAScript 5 Compatibility
27. ECMAScript 6 Styles
28. Testing
29. Performance
30. Resources
31. In the Wild
32. Translation
33. The JavaScript Style Guide Guide
34. Chat With Us About Javascript
35. Contributors
36. License

• 1.1 Primitives: When you access a primitive type you work directly on its value.

  • string
  • number
  • boolean
  • null
  • undefined

  const foo = 1;
  let bar = foo;
  
  bar = 9;
  
  console.log(foo, bar); // => 1, 9

• 1.2 Complex: When you access a complex type you work on a reference to its value.

  • object
  • array
  • function

  const foo = [1, 2];
  const bar = foo;
  
  bar[0] = 9;
  
  console.log(foo[0], bar[0]); // => 9, 9

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• 2.1 Use const for all of your references; avoid using var.

Why? This ensures that you can't reassign your references (mutation), which can lead to bugs and difficult to comprehend code.

```javascript
// bad
var a = 1;
var b = 2;

// good
const a = 1;
const b = 2;
```

• 2.2 If you must mutate references, use let instead of var.

Why? let is block-scoped rather than function-scoped like var.

```javascript
// bad
var count = 1;
if (true) {
  count += 1;
}

// good, use the let.
let count = 1;
if (true) {
  count += 1;
}
```

• 2.3 Note that both let and const are block-scoped.

  // const and let only exist in the blocks they are defined in.
  {
    let a = 1;
    const b = 1;
  }
  console.log(a); // ReferenceError
  console.log(b); // ReferenceError

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• 3.1 Use the literal syntax for object creation.

  // bad
  const item = new Object();
  
  // good
  const item = {};

• 3.2 If your code will be executed in browsers in script context, don't use reserved words as keys. It won't work in IE8. More info. It’s OK to use them in ES6 modules and server-side code.

  // bad
  const superman = {
    default: { clark: 'kent' },
    private: true,
  };
  
  // good
  const superman = {
    defaults: { clark: 'kent' },
    hidden: true,
  };

• 3.3 Use readable synonyms in place of reserved words.

  // bad
  const superman = {
    class: 'alien',
  };
  
  // bad
  const superman = {
    klass: 'alien',
  };
  
  // good
  const superman = {
    type: 'alien',
  };

• 3.4 Use computed property names when creating objects with dynamic property names.

Why? They allow you to define all the properties of an object in one place.

```javascript

function getKey(k) {
  return `a key named ${k}`;
}

// bad
const obj = {
  id: 5,
  name: 'San Francisco',
};
obj[getKey('enabled')] = true;

// good
const obj = {
  id: 5,
  name: 'San Francisco',
  [getKey('enabled')]: true,
};
```