STYLEGUIDE.md

Ember.js JavaScript Style Guide

Table Of Contents

• Objects
• Array
• Variables
• Whitespace
• Commas
• Semicolons
• Block Statements
• Conditional Statements
• Properties
• Functions
• Arrow Functions
• Function Arguments
• Rest Parameters
• Destructuring
• Comments

Objects

• Use literal form for object creation.

var foo = {};

• Pad single-line objects with white-space.

var bar = { color: 'orange' };

Arrays

• Use literal form for array creation (unless you know the exact length).

var foo = [];

• If you know the exact length and know that array is not going to grow, use Array.

var foo = new Array(16);

• Use push to add an item to an array.

var foo = [];
foo.push('bar');

Variables

• Put all non-assigning declarations on one line.

var a, b;

• Use a single var declaration for each assignment.

var a = 1;
var b = 2;

• Declare variables at the top of their scope.

function foo() {
  var bar;

  console.log('foo bar!');

  bar = getBar();
}

Whitespace

• Use soft tabs set to 2 spaces.

function() {
∙∙var name;
}

• Place 1 space before the leading brace.

obj.set('foo', {
  foo: 'bar'
});

test('foo-bar', function() {
});

• No spaces before semicolons.

var foo = {};

• Keep parenthesis adjacent to the function name when declared or called.

function foo() {
}

foo();

Commas

• Skip trailing commas.

var foo = [1, 2, 3];
var bar = { a: 'a' };

• Skip leading commas.

var foo = [
  1,
  2,
  3
];

Semicolons

• Use semicolons.

Block Statements

• Use spaces.

// conditional
if (notFound) {
  return 0;
} else {
  return 1;
}

switch (condition) {
  case 'yes':
    // code
    break;
}

// loops
for (var key in keys) {
  // code
}

for (var i = 0, l = keys.length; i < l; i++) {
  // code
}

while (true) {
  // code
}

try {
  // code that throws an error
} catch(e) {
  // code that handles an error
}

• Opening curly brace should be on the same line as the beginning of a statement or declaration.

function foo() {
  var obj = {
    val: 'test'
  };

  return {
    data: obj
  };
}

if (foo === 1) {
  foo();
}

for (var key in keys) {
  bar(e);
}

while (true) {
  foo();
}

• Keep else and its accompanying braces on the same line.

if (foo === 1) {
  bar = 2;
} else {
  bar = '2';
}

if (foo === 1) {
  bar = 2;
} else if (foo === 2) {
  bar = 1;
} else {
  bar = 3;
}

Conditional Statements

• Use === and !==.
• Use curly braces.

if (notFound) {
  return;
}

• Use explicit conditions.

if (arr.length > 0) {
  // code
}

if (foo !== '') {
  // code
}

Properties

• Use dot-notation when accessing properties.

var foo = {
  bar: 'bar'
};

foo.bar;

• Use [] when accessing properties with a variable.

var propertyName = 'bar';
var foo = {
  bar: 'bar'
};

foo[propertyName];

Functions

• Make sure to name functions when you define them.

function fooBar() {
}

Arrow Functions

• Make sure arrow functions are done on multiple lines.

var foo = [1,2,3,4].map((item) => {
  return item * 2;
});

Function Arguments

arguments object must not be passed or leaked anywhere. See the reference.

• Use a for loop with arguments (instead of slice).

function fooBar() {
  var args = new Array(arguments.length);

  for (var i = 0; i < args.length; ++i) {
    args[i] = arguments[i];
  }

  return args;
}

• Don't re-assign the arguments.

function fooBar() {
  arguments = 3;
}

function fooBar(opt) {
  opt = 3;
}

• Use a new variable if you need to re-assign an argument.

function fooBar(opt) {
  var options = opt;

  options = 3;
}

Rest Parameters

Since Babel implements Rest parameters in a non-leaking matter you should use them whenever applicable.

function foo(...args) {
  args.forEach((item) => {
    console.log(item);
  });
}

Destructuring

When decomposing simple arrays or objects, prefer destructuring.

// array destructuring
var fullName = 'component:foo-bar';
var [
  first,
  last
] = fullName.split(':');

// object destructuring
var person = {
  firstName: 'Stefan',
  lastName: 'Penner'
}

var {
  firstName,
  lastName
} = person;

Comments

• Use YUIDoc comments for documenting functions.
• Use // for single line comments.

function foo() {
  var bar = 5;

  // multiplies `bar` by 2.
  fooBar(bar);

  console.log(bar);
}