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JS Style Guide

First and Foremost

ALWAYS use JSHint on your code.

Note

JSHint may warn about some features of Node.js that aren't present in your typical browser implementation of JavaScript. These can be safely ignored. You can ignore some JSHint warnings permanently with a .jshintrc file.

Variable Formatting:

// Classes: CapitalizedWords
var MyClass = ...

// Variables and Functions: camelCase
var myVariable = ...

// Constants: UPPER_CASE_WITH_UNDERSCORES
const MY_CONST = ...

Indentation

4-space indents (no tabs).

For our projects, always assign var on a newline, not comma separated:

// Bad
var a = 1,
    b = 2,
    c = 3;

// Good
var a = 1;
var b = 2;
var c = 3;

Use [] to assign a new array, not new Array().

Use {} for new objects, as well.

The array literal [] can be used with either a single line or multiple lines, depending how easy it is to read:

// Okay on a single line
var stuff = [1, 2, 3];

// Never on a single line, multiple only
var longerStuff = [
    'some longer stuff',
    'other longer stuff'
];

Never assign multiple variables on the same line

Example of what not to do:

var a = 1, b = 'foo', c = 'don\'t do this';

DO NOT line up variable names

For consistency, don't do this:

var wut    = true;
var boohoo = false;

Semi-colons

Use them.

Even though JavaScript can use automatic semicolon insertion (ASI), you should still use semi-colons to be consistent with the rest of the codebase.

Conditionals and Loops

// Bad
if (something) doStuff()

// Good
if (something) {
    doStuff();
}

Space after keyword, and space before curly

// Bad
if(bad){
    // This is bad
}

// Good
if (something) {
    // This is better
}

Functions

Named Functions

You should assign functions to named symbols, like so:

var updateOnClick = function() { ... };

Here, the function above is known as updateOnClick. The same can be done with objects. In the example below, someObject.updateOnClick is the function:

var someObject = {
    updateOnClick: function() { ... }
};

If you're passing a nontrivial function as an argument, you should name it to avoid obscuring what it's supposed to do.

Don't do this:

obj.forEach(function(item) {
    // A large anonymous function with dozens of lines of code.
    // This makes it hard to understand what the function does
    // without reading through it entirely.
});

Instead, do the following:

var doMagic = function(item) { ... };

obj.forEach(doMagic);

Here, it is easy to see that doMagic gets called for each object.

Whitespacing Functions

Do not put a space between "function" and the opening parenthesis. Do put a space after the closing parenthesis and before the opening curly brace:

var method = function(argOne, argTwo) {
    // Do something
};

Anonymous Functions

Anonymous functions are fine if they have a small amount of code in them. See the :ref:`named-functions` section for more information about inferred function names for anonymous functions.

Operators

Always use strict equality (===).

The only exception to this rule is when testing for null and undefined.

Example:

if (value != null) {
    // This is an exception to the rule. Usually you'd use !==
}

Quotes

Always use single quotes: 'not double'

There is only one exception: "don't escape single quotes in strings; use double quotes instead"

Comments

For Node.js functions, always provide a clear comment in this format:

/* Briefly explains what this does
 * Expects: whatever parameters
 * Returns: whatever it returns
 */

If your comment is really long, use the format mentioned above (/* ... */). Otherwise make short comments like so:

// This is a short comment that ends in a period.

Ternaries

Avoid using the ternary operator ((condition) ? (true) : (false)).

If using the ternary operator makes a line particularly complex, or would require using multiple lines, don't use it:

// Bad
var foo = (user.lastLogin > new Date().getTime() - 16000) ? user.lastLogin - 24000 : 'wut';

// Good
return user.isLoggedIn ? 'yay' : 'boo';

General Good Practices

  • Don't repeat yourself! If you see yourself repeating something that could be a constant, refactor it as a single constant declaration at the top of the file.

  • Try caching your regular expressions (regex) by declaring them as constants.

  • Always check for truthiness:

    // Bad
    if (blah !== false) { ... }
    
    // Good
    if (blah) { ... }
  • If one line in your code is really long, you should probably refactor it. If this isn't possible, try breaking it up into multiple lines.

  • Try to keep within the 80-column limit (but if you go a bit past it's not a big deal). Indent the subsequent lines one indent (2-spaces) in.

  • If it looks too clever, it probably is, so just make it simple.

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