• Rick Waldron @rwaldron, github
• Mathias Bynens @mathias, github
• Schalk Neethling @ossreleasefeed, github
• Kit Cambridge @kitcambridge, github
• Raynos github
• Matias Arriola @MatiasArriola, github
• Idan Gazit @idangazit, github
• Leo Balter @leobalter, github
• Breno Oliveira @garu_rj, github
• Leo Beto Souza @leobetosouza, github
• EngForDev engfordev - Hwan Min Hong / MinTaek Kwon @leoinsight / Tw Shim @marocchino, github / Nassol Kim @nassol99, github / Juntai Park @rkJun, github / Minkyu Shim / Gangmin Won / Justin Yoo @justinchronicle / Daeyup Lee

"Part of being a good steward to a successful project is realizing that writing code for yourself is a Bad Idea™. If thousands of people are using your code, then write your code for maximum clarity, not your personal preference of how to get clever within the spec." - Idan Gazit

• French
• Spanish
• Portuguese - Brazil
• Korean

• jsPerf
• jsFiddle
• jsbin
• JavaScript Lint (JSL)
• jshint
• jslint

Leveraging Code Quality Tools by Anton Kovalyov

http://es5.github.com/

The following should be considered 1) incomplete, and 2) REQUIRED READING. I don't always agree with the style written by the authors below, but one thing is certain: They are consistent. Furthermore, these are authorities on the language.

• Eloquent JavaScript
• JavaScript, JavaScript
• Rebecca Murphey or Adventures in JavaScript Development
• Perfection Kills
• Douglas Crockford's Wrrrld Wide Web

Projects should always attempt to include some generic means by which source can be linted, tested and compressed in preparation for production use. For this task, grunt by Ben Alman is second to none and has officially replaced the "kits/" directory of this repo.

Projects must include some form of unit, reference, implementation or functional testing. Use case demos DO NOT QUALIFY as "tests". The following is a list of test frameworks, none of which are endorsed more than the other.

• QUnit
• Jasmine
• Vows
• Mocha
• Hiro
• JsTestDriver

• Whitespace
• Beautiful Syntax
• Type Checking (Courtesy jQuery Core Style Guidelines)
• Conditional Evaluation
• Practical Style
• Naming
• Misc
• Native & Host Objects
• Comments
• One Language Code

The following sections outline a reasonable style guide for modern JavaScript development and are not meant to be prescriptive. The most important take-away is the law of code style consistency. Whatever you chose as the style for your project should be considered law. Link to this document as a statement of your project's commitment to code style consistency, readability and maintainability.

1. Whitespace

• Never mix spaces and tabs.
• When beginning a project, before you write any code, choose between soft indents (spaces) or real tabs, consider this law.
  • For readability, I always recommend setting your editor's indent size to two characters — this means two spaces or two spaces representing a real tab.
• If your editor supports it, always work with the "show invisibles" setting turned on. The benefits of this practice are:
  • Enforced consistency
  • Eliminating end of line whitespace
  • Eliminating blank line whitespace
  • Commits and diffs that are easier to read

2. Beautiful Syntax

   A. Parens, Braces, Linebreaks

   // if/else/for/while/try always have spaces, braces and span multiple lines
   // this encourages readability
   
   // 2.A.1.1
   // Examples of really cramped syntax
   
   if(condition) doSomething();
   
   while(condition) iterating++;
   
   for(var i=0;i<100;i++) someIterativeFn();
   
   
   // 2.A.1.1
   // Use whitespace to promote readability
   
   if ( condition ) {
     // statements
   }
   
   while ( condition ) {
     // statements
   }
   
   for ( var i = 0; i < 100; i++ ) {
     // statements
   }
   
   // Even better:
   
   var i,
     length = 100;
   
   for ( i = 0; i < length; i++ ) {
     // statements
   }
   
   // Or...
   
   var i = 0,
     length = 100;
   
   for ( ; i < length; i++ ) {
     // statements
   }
   
   var prop;
   
   for ( prop in object ) {
     // statements
   }
   
   
   if ( true ) {
     // statements
   } else {
     // statements
   }

   B. Assignments, Declarations, Functions ( Named, Expression, Constructor )

   // 2.B.1.1
   // Variables
   var foo = "bar",
     num = 1,
     undef;
   
   // Literal notations:
   var array = [],
     object = {};
   
   
   // 2.B.1.2
   // Using only one `var` per scope (function) promotes readability
   // and keeps your declaration list free of clutter (also saves a few keystrokes)
   
   // Bad
   var foo = "";
   var bar = "";
   var qux;
   
   // Good
   var foo = "",
     bar = "",
     quux;
   
   // or..
   var // Comment on these
   foo = "",
   bar = "",
   quux;
   
   // 2.B.1.3
   // var statements should always be in the beginning of their respective scope (function).
   // Same goes for const and let from ECMAScript 6.
   
   // Bad
   function foo() {
   
     // some statements here
   
     var bar = "",
       qux;
   }
   
   // Good
   function foo() {
     var bar = "",
       qux;
   
     // all statements after the variables declarations.
   }

   // 2.B.2.1
   // Named Function Declaration
   function foo( arg1, argN ) {
   
   }
   
   // Usage
   foo( arg1, argN );
   
   
   // 2.B.2.2
   // Named Function Declaration
   function square( number ) {
     return number * number;
   }
   
   // Usage
   square( 10 );
   
   // Really contrived continuation passing style
   function square( number, callback ) {
     callback( number * number );
   }
   
   square( 10, function( square ) {
     // callback statements
   });
   
   
   // 2.B.2.3
   // Function Expression
   var square = function( number ) {
     // Return something valuable and relevant
     return number * number;
   };
   
   // Function Expression with Identifier
   // This preferred form has the added value of being
   // able to call itself and have an identity in stack traces:
   var factorial = function factorial( number ) {
     if ( number < 2 ) {
       return 1;
     }
   
     return number * factorial( number-1 );
   };
   
   
   // 2.B.2.4
   // Constructor Declaration
   function FooBar( options ) {
   
     this.options = options;
   }
   
   // Usage
   var fooBar = new FooBar({ a: "alpha" });
   
   fooBar.options;
   // { a: "alpha" }

   C. Exceptions, Slight Deviations

   // 2.C.1.1
   // Functions with callbacks
   foo(function() {
     // Note there is no extra space between the first paren
     // of the executing function call and the word "function"
   });
   
   // Function accepting an array, no space
   foo([ "alpha", "beta" ]);
   
   // 2.C.1.2
   // Function accepting an object, no space
   foo({
     a: "alpha",
     b: "beta"
   });
   
   // Inner grouping parens, no space
   if ( !("foo" in obj) ) {
   
   }

   D. Consistency Always Wins

   In sections 2.A-2.C, the whitespace rules are set forth as a recommendation with a simpler, higher purpose: consistency. It's important to note that formatting preferences, such as "inner whitespace" should be considered optional, but only one style should exist across the entire source of your project.

   // 2.D.1.1
   
   if (condition) {
     // statements
   }
   
   while (condition) {
     // statements
   }
   
   for (var i = 0; i < 100; i++) {
     // statements
   }
   
   if (true) {
     // statements
   } else {
     // statements
   }

   E. End of Lines and Empty Lines

   Whitespace can ruin diffs and make changesets impossible to read. Consider incorporating a pre-commit hook that removes end-of-line whitespace and blanks spaces on empty lines automatically.

3. Type Checking (Courtesy jQuery Core Style Guidelines)

   A. Actual Types

   String:

    `typeof variable === "string"`
   

   Number:

    `typeof variable === "number"`
   

   Boolean:

    `typeof variable === "boolean"`
   

   Object:

    `typeof variable === "object"`
   

   Array:

    `Array.isArray(arrayObject)`
    (wherever possible)
   

   null:

    `variable === null`
   

   null or undefined:

    `variable == null`
   

   undefined:

   Global Variables:

    `typeof variable === "undefined"`
   

   Local Variables:

    `variable === undefined`
   

   Properties: object.prop === undefined object.hasOwnProperty( prop ) "prop" in object

   B. Coerced Types

   Consider the implications of the following...

   Given this HTML:

   <input type="text" id="foo-input" value="1">

   // 3.B.1.1
   
   // `foo` has been declared with the value `0` and its type is `number`
   var foo = 0;
   
   // typeof foo;
   // "number"
   ...
   
   // Somewhere later in your code, you need to update `foo`
   // with a new value derived from an input element
   
   foo = document.getElementById("foo-input").value;
   
   // If you were to test `typeof foo` now, the result would be `string`
   // This means that if you had logic that tested `foo` like:
   
   if ( foo === 1 ) {
   
     importantTask();
   
   }
   
   // `importantTask()` would never be evaluated, even though `foo` has a value of "1"
   
   
   // 3.B.1.2
   
   // You can preempt issues by using smart coercion with unary + or - operators:
   
   foo = +document.getElementById("foo-input").value;
         ^ unary + operator will convert its right side operand to a number
   
   // typeof foo;
   // "number"
   
   if ( foo === 1 ) {
   
     importantTask();
   
   }
   
   // `importantTask()` will be called

   Here are some common cases along with coercions:

   // 3.B.2.1
   
   var number = 1,
     string = "1",
     bool = false;
   
   number;
   // 1
   
   number + "";
   // "1"
   
   string;
   // "1"
   
   +string;
   // 1
   
   +string++;
   // 1
   
   string;
   // 2
   
   bool;
   // false
   
   +bool;
   // 0
   
   bool + "";
   // "false"

   // 3.B.2.2
   
   var number = 1,
     string = "1",
     bool = true;
   
   string === number;
   // false
   
   string === number + "";
   // true
   
   +string === number;
   // true
   
   bool === number;
   // false
   
   +bool === number;
   // true
   
   bool === string;
   // false
   
   bool === !!string;
   // true

   // 3.B.2.3
   
   var array = [ "a", "b", "c" ];
   
   !!~array.indexOf( "a" );
   // true
   
   !!~array.indexOf( "b" );
   // true
   
   !!~array.indexOf( "c" );
   // true
   
   !!~array.indexOf( "d" );
   // false
   
   
   var num = 2.5;
   
   parseInt( num, 10 );
   
   // is the same as...
   
   ~~num;

4. Conditional Evaluation

   // 4.1.1
   // When only evaluating that an array has length,
   // instead of this:
   if ( array.length > 0 ) ...
   
   // ...evaluate truthiness, like this:
   if ( array.length ) ...
   
   
   // 4.1.2
   // When only evaluating that an array is empty,
   // instead of this:
   if ( array.length === 0 ) ...
   
   // ...evaluate truthiness, like this:
   if ( !array.length ) ...
   
   
   // 4.1.3
   // When only evaluating that a string is not empty,
   // instead of this:
   if ( string !== "" ) ...
   
   // ...evaluate truthiness, like this:
   if ( string ) ...
   
   
   // 4.1.4
   // When only evaluating that a string _is_ empty,
   // instead of this:
   if ( string === "" ) ...
   
   // ...evaluate falsy-ness, like this:
   if ( !string ) ...
   
   
   // 4.1.5
   // When only evaluating that a reference is true,
   // instead of this:
   if ( foo === true ) ...
   
   // ...evaluate like you mean it, take advantage of it's primitive capabilities:
   if ( foo ) ...
   
   
   // 4.1.6
   // When evaluating that a reference is false,
   // instead of this:
   if ( foo === false ) ...
   
   // ...use negation to coerce a true evaluation
   if ( !foo ) ...
   
   // ...Be careful, this will also match: 0, "", null, undefined, NaN
   // If you _MUST_ test for a boolean false, then use
   if ( foo === false ) ...
   
   
   // 4.1.7
   // When only evaluating a ref that might be null or undefined, but NOT false, "" or 0,
   // instead of this:
   if ( foo === null || foo === undefined ) ...
   
   // ...take advantage of == type coercion, like this:
   if ( foo == null ) ...
   
   // Remember, using == will match a `null` to BOTH `null` and `undefined`
   // but not `false`, "" or 0
   null == undefined

   ALWAYS evaluate for the best, most accurate result - the above is a guideline, not a dogma.

   // 4.2.1
   // Type coercion and evaluation notes
   
   Prefer `===` over `==` (unless the case requires loose type evaluation)
   
   === does not coerce type, which means that:
   
   "1" === 1;
   // false
   
   == does coerce type, which means that:
   
   "1" == 1;
   // true
   
   
   // 4.2.2
   // Booleans, Truthies & Falsies
   
   Booleans: true, false
   
   Truthy are: "foo", 1
   
   Falsy are: "", 0, null, undefined, NaN, void 0

5. Practical Style

// 5.1.1
// A Practical Module

(function( global ) {
  var Module = (function() {

    var data = "secret";

    return {
      // This is some boolean property
      bool: true,
      // Some string value
      string: "a string",
      // An array property
      array: [ 1, 2, 3, 4 ],
      // An object property
      object: {
        lang: "en-Us"
      },
      getData: function() {
        // get the current value of `data`
        return data;
      },
      setData: function( value ) {
        // set the value of `data` and return it
        return ( data = value );
      }
    };
  })();

  // Other things might happen here

  // expose our module to the global object
  global.Module = Module;

})( this );

// 5.2.1
// A Practical Constructor

(function( global ) {

  function Ctor( foo ) {

    this.foo = foo;

    return this;
  }

  Ctor.prototype.getFoo = function() {
    return this.foo;
  };

  Ctor.prototype.setFoo = function( val ) {
    return ( this.foo = val );
  };


  // To call constructor's without `new`, you might do this:
  var ctor = function( foo ) {
    return new Ctor( foo );
  };


  // expose our constructor to the global object
  global.ctor = ctor;

})( this );

6. Naming

You are not a human code compiler/compressor, so don't try to be one.

The following code is an example of egregious naming:

// 6.1.1
// Example of code with poor names

function q(s) {
  return document.querySelectorAll(s);
}
var i,a=[],els=q("#foo");
for(i=0;i<els.length;i++){a.push(els[i]);}

Without a doubt, you've written code like this - hopefully that ends today.

Here's the same piece of logic, but with kinder, more thoughtful naming (and a readable structure):

// 6.2.1
// Example of code with improved names

function query( selector ) {
  return document.querySelectorAll( selector );
}

var idx = 0,
  elements = [],
  matches = query("#foo"),
  length = matches.length;

for( ; idx < length; idx++ ){
  elements.push( matches[ idx ] );
}

A few additional naming pointers:

// 6.3.1
// Naming strings

`dog` is a string


// 6.3.2
// Naming arrays

`dogs` is an array of `dog` strings


// 6.3.3
// Naming functions, objects, instances, etc

camelCase; function and var declarations


// 6.3.4
// Naming constructors, prototypes, etc.

PascalCase; constructor function


// 6.3.5
// Naming regular expressions

rDesc = //;


// 6.3.6
// From the Google Closure Library Style Guide

functionNamesLikeThis;
variableNamesLikeThis;
ConstructorNamesLikeThis;
EnumNamesLikeThis;
methodNamesLikeThis;
SYMBOLIC_CONSTANTS_LIKE_THIS;

7. Misc

This section will serve to illustrate ideas and concepts that should not be considered dogma, but instead exists to encourage questioning practices in an attempt to find better ways to do common JavaScript programming tasks.

A. Using switch should be avoided, modern method tracing will blacklist functions with switch statements

There seems to be drastic improvements to the execution of switch statements in latest releases of Firefox and Chrome. http://jsperf.com/switch-vs-object-literal-vs-module

Notable improvements can be witnesses here as well: rwaldron#13

// 7.A.1.1
// An example switch statement

switch( foo ) {
  case "alpha":
    alpha();
    break;
  case "beta":
    beta();
    break;
  default:
    // something to default to
    break;
}

// 7.A.1.2
// A better approach would be to use an object literal or even a module:

var switchObj = {
  alpha: function() {
    // statements
    // a return
  },
  beta: function() {
    // statements
    // a return
  },
  _default: function() {
    // statements
    // a return
  }
};

var switchModule = (function () {
  return {
    alpha: function() {
      // statements
      // a return
    },
    beta: function() {
      // statements
      // a return
    },
    _default: function() {
      // statements
      // a return
    }
  };
})();


// 7.A.1.3
// If `foo` is a property of `switchObj` or `switchModule`, execute as a method...

( Object.hasOwnProperty.call( switchObj, foo ) && switchObj[ foo ] || switchObj._default )( args );

( Object.hasOwnProperty.call( switchObj, foo ) && switchModule[ foo ] || switchModule._default )( args );

// If you know and trust the value of `foo`, you could even omit the OR check
// leaving only the execution:

switchObj[ foo ]( args );

switchModule[ foo ]( args );


// This pattern also promotes code reusability.

B. Early returns promote code readability with negligible performance difference

// 7.B.1.1
// Bad:
function returnLate( foo ) {
  var ret;

  if ( foo ) {
    ret = "foo";
  } else {
    ret = "quux";
  }
  return ret;
}

// Good:

function returnEarly( foo ) {

  if ( foo ) {
    return "foo";
  }
  return "quux";
}

8. Native & Host Objects

The basic principal here is:

To reinforce this concept, please watch the following presentation:

http://blip.tv/jsconf/jsconf2011-andrew-dupont-everything-is-permitted-extending-built-ins-5211542

9. Comments

• JSDoc style is good (Closure Compiler type hints++)
• Single line above the code that is subject
• Multiline is good
• End of line comments are prohibited!

10. One Language Code

Programs should be written in one language, whatever that language may be, as dictated by the maintainer or maintainers.

Any project that cites this document as its base style guide will not accept comma first code formatting, unless explicitly specified otherwise by that project's author.