A mostly reasonable approach to JavaScript

For the ES5-only guide click here[1].

Table of Contents

Types

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

    • string
    • number
    • boolean
    • null
    • undefined
    const ; bar foo; bar ; console(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 [, ]; const foo; bar[] ; console(foo[], bar[]); / / = > 9, 9

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References

  • 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.

      // bad
   a  ;
   b  ;

  // good
  const   ;
  const   ;

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

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

      // bad
   count  ;
   () {
    count  ;
  }

  // good, use the let.
   count  ;
   () {
    count  ;
  }

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

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

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Objects

  • 3.1 Use the literal syntax for object creation.

    // bad
const    Object();

// good
const   {};

  • 3.2 If your code will be executed in script context, are browsers It won’t work in IE8.more info[2]. It’s OK to use them in ES6 modules and server-side code.

    // bad
const superman  {
  default { clark  },
  private ,
};

// good
const superman  {
  defaults { clark  },
  hidden ,
};

  • 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.

      function getKey() {
    return a key named ;
  }

  // bad
  const   {
    id ,
    name San Francisco,
  };
  obj[getKey(enabled)]  ;

  // good
  const   {
    id ,
    name San Francisco,
    [getKey(enabled)] ,
  };

  • 3.5 Use object method shorthand.

    // bad const { value , addValue function (value) { return atom.value value; }}; // good const { value , addValue(value) { return atom.value value; }};

  • 3.6 Use Property value dictate.

    Why? It is shorter to write and descriptive.

      const lukeSkywalker  Luke Skywalker;

  // bad
  const   {
    lukeSkywalker lukeSkywalker,
  };

  // good
  const   {
    lukeSkywalker,
  };

  • 3.7 Group your sleep properties at the beginning of your object declaration.

    Why? It’s easier to tell which properties are using the shorthand.

      const anakinSkywalker  Anakin Skywalker;
  const lukeSkywalker  Luke Skywalker;

  // bad
  const   {
    episodeOne ,
    twoJediWalkIntoACantina ,
    lukeSkywalker,
    episodeThree ,
    mayTheFourth ,
    anakinSkywalker,
  };

  // good
  const   {
    lukeSkywalker,
    anakinSkywalker,
    episodeOne ,
    twoJediWalkIntoACantina ,
    episodeThree ,
    mayTheFourth ,
  };

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Arrays

  • 4.1 Use the literal syntax for array creation.

    // bad
const items   Array();

// good
const items  [];

  • 4.2 Use Array#push instead of direct assignment to add items to an array.

    const someStack  [];


// bad
someStack[someStack.length]  abracadabra;

// good
someStack.(abracadabra);

  • 4.3 Use array Spreads… to copy arrays.

    // bad
const   items.length;
const itemsCopy  [];
 i;

 (i  ; i  len; i) {
  itemsCopy[i]  items[i];
}

// good
const itemsCopy  [...items];

  • 4.4 To convert an array-like object to an array, use Array#from.

    const   document.querySelectorAll();
const nodes  Array.from(foo);

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Destructuring

  • 5.1 Use object destructuring when accessing and using multiple properties of an object.

    Why? Destructuring saves you from creating temporary references for those properties.

      // bad
  function getFullName() {
    const firstName  user.firstName;
    const lastName  user.lastName;

    return firstName lastName;
  }

  // good
  function getFullName() {
    const { firstName, lastName }  obj;
    return firstName lastName;
  }

  // best
  function getFullName({ firstName, lastName }) {
    return firstName lastName;
  }

  • 5.2 the Use of array destructuring.

    const   [, , , ];

// bad
const first  arr[];
const second  arr[];

// good
const [first, second]  arr;

  • 5.3 Use object destructuring for multiple return values, not array destructuring.

    Why? You can add new properties over time or change the order of things without breaking call sites.

      // bad
  function processInput(input) {
    // then a miracle occurs
    return [left, right, top, bottom];
  }

  // the caller needs to think about the order of return data
  const [left, __, top]  processInput(input);

  // good
  function processInput(input) {
    // then a miracle occurs
    return { left, right, top, bottom };
  }

  // the caller selects only the data they need
  const { left, right }  processInput(input);

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Strings

  • 6.1 Use single quotes “for strings.

    // bad
const   Capt. Janeway;

// good
const   Capt. Janeway;

  • 6.2 Strings longer than 80 characters should be written across multiple lines using string concatenation.

  • 6.3 Note: If overused, long strings with concatenation could impact performance. JsPerf [3] & Discussion[4].

    // bad const errorMessage This is a super long error that was thrown because of Batman. When you stop to think about how  Batman had anything to do with this, you would get nowhere fast.; // bad const errorMessage This is a super long error that was thrown because \ of Batman. When you stop to think about how Batman had anything to do \ with this, you would get nowhere \ fast.; // good const errorMessage This is a super long error that was thrown because of Batman. When you stop to think about how Batman had anything to do with this, you would get nowhere fast.;

  • 6.4 When programmatically building up strings, use template strings instead of concatenation.

    Why? Template strings give you a readable, concise syntax with proper newlines and string interpolation features.

    // bad function sayHi() { return How are you, name ; } // bad function sayHi() { return [How are you, , name, ].(); } // good function sayHi() { return How are you, ? ; }

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Functions

  • Use function declarations instead of function expressions.

    Why? Function declarations are named, so they’re easier to identify in call stacks. Also, the whole body of a function declaration is hoisted, whereas only the reference of a function expression is hoisted. This rule makes it possible to always use Arrow Functions in place of function expressions.

      // bad
  const   function () {
  };

  // good
  function () {
  }

  • 7.2 the Function expressions:

    // immediately-invoked function expression (IIFE) (() => { console(Welcome to the Internet. Please follow me.); }) ();

  • Never declare a function in a non-function block (if, while, etc). Assign the function to a variable instead. Browsers will allow you to do it, but they all interpret it differently, which is bad news bears.

  • Note 7.4: ECMA-262 defines a block as a list of statements. A function declaration is not a statement. Read ECMA-262’s note on this issue.

    // bad
 (currentUser) {
  function () {
    console(Nope.);
  }
}

// good
 test;
 (currentUser) {
  test  () => {
    console();
  };
}

  • 7.5 Never name a parameter arguments. This will take precedence over the arguments object that is given to every function scope.

    // bad function (, options, arguments) { // ... stuff... } // good function (, options, ) { // ... stuff... }

  • 7.6 Never use arguments, opt to use rest syntax… instead.

    Why? . is explicit about which arguments you want pulled. Plus rest arguments are a real Array and not Array-like like arguments.

      // bad
  function concatenateAll() {
    const   Array.prototype.slice.(arguments);
    return args.();
  }

  // good
  function concatenateAll(...) {
    return args.();
  }

  • 7.7 Use default parameter syntax rather than mutating function arguments.

    // really bad function handleThings() { // No! We shouldn't mutate function arguments. // Double bad: if opts is falsy it'll be set to an object which may // be what you want but it can introduce subtle bugs. opts opts {};  / /... } // still bad function handleThings() { (opts ) { opts {}; } / /... } // good function handleThings( = {}) { // ... }

  • 7.8 Avoid side effects with default parameters

    Why? They are confusing to reason about.

     b  ;
// bad
function count( = b++) {
  console(a);
}
count();  
count();  
count(); 
count();

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Arrow Functions

  • 8.1 When you must use function expressions (as when passing an anonymous function), use arrow function notation.

    Why? It creates a version of the function that executes in the context of this, which is usually what you want, and is a more concise syntax.

    Why not? If you have a fairly complicated function, you might move that logic out into its own function declaration.

      // bad
  [, , ].map(function () {
    return x  x;
  });

  // good
  [, , ].map(() => {
    return x  x;
  });

  • 8.2 If the function body fits on one line and there is only a single argument, feel free to omit the braces and parentheses, and use the implicit return. Otherwise, add the parentheses, braces, and use a return statement.

    Why? Syntactic sugar. It reads well when multiple functions are chained together.

    Why not? If you plan on returning an object.

    // good [, , ].map(x => x x); // good [, , ].reduce((total, ) => { return total n; });

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Constructors

  • 9.1 Always use class. Avoid manipulating prototype directly.

    Why? class syntax is more concise and easier to reason about.

    // bad function Queue(contents = []) { ._queue [...contents]; } Queue.prototype. function() { const value ._queue[]; ._queue.splice(, ); return value; } // good class Queue { constructor(contents = []) { ._queue [...contents]; } () { const value ._queue[]; ._queue.splice(, ); return value; }}

  • 9.2 Use extends for inheritance.

    Why? It is a built-in way to inherit prototype functionality without breaking instanceof.

    // bad const inherits require(inherits); function PeekableQueue(contents) { Queue.apply(, contents); } inherits(PeekableQueue, Queue); PeekableQueue.prototype. function() { return ._queue[]; } // good class PeekableQueue extends Queue { () { return ._queue[]; }}

  • 9.3 Methods can return this to help with method chaining.

    // bad
.prototype.  function() {
  .jumping  ;
  return ;
};

.prototype.setHeight  function(height) {
  .height  height;
};

const    ();
luke.jump(); // => true
luke.setHeight(); // => undefined

// good
class  {
  () {
    .jumping  ;
    return ;
  }

  setHeight(height) {
    .height  height;
    return ;
  }
}

const    ();

luke.jump()
  .setHeight();

  • 9.4 It’s okay to write a custom toString() method, just make sure it works successfully and causes no side effects.

    class { constructor(options = {}) { . options. no name; } getName() { return .; } toString() { return Jedi - .getName(); }}

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Modules

  • 10.1 Always use modules (import/export) over a non-standard module system. You can always transpile to your preferred module system.

    Why? Modules are the future, let’s start using the future now.

      // bad
  const AirbnbStyleGuide  require(./AirbnbStyleGuide);
  module.exports  AirbnbStyleGuide.es6;

  
  import AirbnbStyleGuide  ./AirbnbStyleGuide;
  export default AirbnbStyleGuide.es6;

  // best
  import { es6 }  ./AirbnbStyleGuide;
  export default es6;

  • 10.2 Do not use wildcard imports.

    Why? This makes sure you have a single default export.

      // bad
  import *  AirbnbStyleGuide  ./AirbnbStyleGuide;

  // good
  import AirbnbStyleGuide  ./AirbnbStyleGuide;

  • Do not export directly from an import.

    Why? Although the one-liner is concise, having one clear way to import and one clear way to export makes things consistent.

      // bad
  // filename es6.js
  export { es6 as default }  ./airbnbStyleGuide;

  // good
  // filename es6.js
  import { es6 }  ./AirbnbStyleGuide;
  export default es6;

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Iterators and Generators

  • 11.1 Don’t use iterators. Prefer JavaScript’s higher-order functions like map() and reduce() instead of loops like for-of.

    Why? This enforces our immutable rule. Dealing with pure functions that return values is easier to reason about than side-effects.

      const numbers  [, , , , ];

  // bad
   sum  ;
   ( num  numbers) {
    sum  num;
  }

  sum  ;

  // good
   sum  ;
  numbers.forEach(() => sum  num);
  sum  ;

  // best (use the functional force)
  const   numbers.reduce((total, ) => total  num, );
  sum  ;

  • 11.2 Don’t use generators for now

    Why? They don’t transpile well to ES5.

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Properties

  • 12.1 Use dot notation when accessing properties.

    const   {
  jedi ,
  age ,
};

// bad
const isJedi  luke[];

// good
const isJedi  luke.jedi;

  • 12.2 Use subscript notation [] when accessing properties with a variable.

    const   {
  jedi ,
  age ,
};

function getProp() {
  return luke[prop];
}

const isJedi  getProp();

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Variables

  • 13.1 Always use const to declare variables. Not doing so will result in global variables. We want to avoid polluting the global namespace. Captain Planet warned us of that.

    // bad
superPower   SuperPower();

// good
const superPower   SuperPower();

  • 13.2 Use one const declaration per variable

    Why? It’s easier to add new variable declarations this way, and you never have to worry about swapping out a ; for a , or introducing punctuation-only diffs.

    // bad
const items  getItems(),
    goSportsTeam  ,
    dragonball  ;

// bad
// (compare to above, and try to spot the mistake)
const items  getItems(),
    goSportsTeam  ;
    dragonball  ;

// good
const items  getItems();
const goSportsTeam  ;
const dragonball  ;

  • 13.3 Group all your consts and then group all your lets.

    Why? This is helpful when later on you might need to assign a variable depending on one of the previous assigned variables.

      // bad
   i, len, dragonball,
      items  getItems(),
      goSportsTeam  ;

  // bad
   i;
  const items  getItems();
   dragonball;
  const goSportsTeam  ;
   len;

  // good
  const goSportsTeam  ;
  const items  getItems();
   dragonball;
   i;
   length;

  • 13.4 Assign variables where you need them, but place them in a reasonable place.

    Why? let and const are block scoped and not function scoped.

    // good function() { (); console(doing stuff..) ; / /.. other stuff.. const getName(); (name ) { return false; } return name; } // bad - unnecessary function call function(hasName) { const getName(); (hasName) { return false; } .setFirstName(name); return ; } // good function(hasName) { (hasName) { return false; } const getName(); .setFirstName(name); return ; }

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Hoisting

  • 14.1 var declarations get hoisted to the top of their scope, their assignment does not. const and let declarations are blessed with a new concept called Temporal Dead Zones (TDZ). It’s important to know why typeof is no longer safe[5].

    // we know this wouldn't work (assuming there
// is no notDefined global variable)
function example() {
  console(notDefined); // => throws a ReferenceError
}

// creating a variable declaration after you
// reference the variable will work due to
// variable hoisting. Note: the assignment
// value of `true` is not hoisted.
function example() {
  console(declaredButNotAssigned); // => undefined
   declaredButNotAssigned  ;
}

// The interpreter is hoisting the variable
// declaration to the top of the scope,
// which means our example could be rewritten as:
function example() {
   declaredButNotAssigned;
  console(declaredButNotAssigned); // => undefined
  declaredButNotAssigned  ;
}

// using const and let
function example() {
  console(declaredButNotAssigned); // => throws a ReferenceError
  console(typeof declaredButNotAssigned); // => throws a ReferenceError
  const declaredButNotAssigned  ;
}

  • 14.2 Anonymous function hoist their variable name, but not the function assignment.

    function example() {
  console(anonymous); // => undefined

  anonymous(); // => TypeError anonymous is not a function

   anonymous  function() {
    console(anonymous function expression);
  };
}

  • 14.3 Named function expressions the variable name, not the function name or the function body.

    function example() { console(named); // => undefined named(); // => TypeError named is not a function superPower(); // => ReferenceError superPower is not defined named function superPower() { console(Flying); }; } // the same is true when the function name // is the same as the variable name. function example() { console(named); // => undefined named(); // => TypeError named is not a function named function named() { console(named); }}

  • Function declarations their name and the Function body.

    function example() { superPower(); // => Flying function superPower() { console(Flying); }}

  • For more information refer to JavaScript Scoping & Hoisting[6] by Ben Cherry[7].

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Comparison Operators & Equality

  • 15.1 Use = = = and ! = = over = = and ! =.

  • 15.2 Conditional statements such as the if statement evaluate their expression using the ToBoolean abstract method and always follow these simple rules:

    • Objects evaluate to true
    • Undefined evaluates to false
    • Null evaluates to false
    • Booleans evaluate to the value of the boolean
    • Numbers evaluate to false if +0, -0, or NaN, otherwise true
    • Strings evaluate to false if an empty string ' ', otherwise true
     ([]) {
  // true
  // An array is an object, objects evaluate to true
}

  • 15.3 Use shortcuts.

    // bad (name ) { // ... stuff... } // good (name) { // ... stuff... } // bad (collection.length ) { // ... stuff... } // good (collection.length) { // ... stuff... }

  • 15.4 For more information see Truth Equality and JavaScript by Angus Croll.

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Blocks

  • 16.1 Use braces with all multi-line blocks.

    // bad
 (test)
  return false;

// good
 (test) return false;

// good
 (test) {
  return false;
}

// bad
function() { return false; }

// good
function() {
  return false;
}

  • 16.2 If you’re using multi-line blocks with if and else, put else on the same line as your if block’s closing brace.

    // bad
 (test) {
  thing1();
  thing2();
}
 {
  thing3();
}

// good
 (test) {
  thing1();
  thing2();
}  {
  thing3();
}

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Comments

  • 17.1 Use / * *… */ for multi-line comments. Include a description, specify types and values for all parameters and return values.

    // bad // make() returns a new element // based on the passed in tag name // @param {String} tag // @return {Element} element function () { // ... stuff... return element; } // good * make() returns a new element * based on the passed in tag name * @param {String} tag * @return {Element} element function () { // ... stuff... return element; }

  • 17.2 Use // for single line comments. Place single line comments on a newline above the subject of the comment. Put an empty line before the comment.

    // bad const active ; // is current tab // good // is current tab const active ; // bad function getType() { console(fetching type...) ; // set the default type to 'no type' const ._type no type; return type; } // good function getType() { console(fetching type...) ; // set the default type to 'no type' const ._type no type; return type; }

  • 17.3 Prefixing your comments with FIXME or TODO helps other developers quickly understand if you’re pointing out a problem that needs to be revisited, or if you’re suggesting a solution to the problem that needs to be implemented. These are different than regular comments because they are actionable. The actions are FIXME -- need to figure this out or TODO -- need to implement.

  • 17.4 Use // FIXME: to annotate problems.

    class Calculator { constructor() { // FIXME: shouldn't use a global here total ; }}

  • 17.5 Use // TODO: to annotate solutions to problems.

    class Calculator { constructor() { // TODO: total should be configurable by an options param .total ; }}

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Whitespace

  • 18.1 Use soft tabs set to 2 spaces.

    // bad function() {∙∙∙const; } // bad function() {∙const; } // good function() {∙∙const; }

  • 18.2 Place 1 space before the leading brace

    // bad
function (){
  console();
}

// good
function () {
  console();
}

// bad
dog.set(,{
  age 1 year,
  breed Bernese Mountain Dog,
});

// good
dog.set(, {
  age 1 year,
  breed Bernese Mountain Dog,
});

  • 18.3 Place 1 space before the opening parenthesis in control statements (if, while etc.). Place no space before the argument list in function calls and declarations.

    // bad (isJedi) { fight (); } // good (isJedi) { fight(); } // bad function fight () { console (Swooosh!) ; } // good function fight() { console(Swooosh!) ; }

  • 18.4 Set off operators with spaces.

    // bad
const y;

// good
const   y  ;

  • 18.5 End files with a single newline character.

    // bad (function(global) { // ... stuff... }) ();

    // bad (function(global) { // ... stuff... }) (); ↵ ↵

    // good (function(global) { // ... stuff... }) (); ↵

  • 18.5 Use indentation when making long method chains. Use a leading dot, which emphasizes that the line is a method call, not a new statement.

    // bad
$(#items).(.selected).highlight().end().(.open).updateCount();

// bad
$(#items).
  (.selected).
    highlight().
    end().
  (.open).
    updateCount();

// good
$(#items)
  .(.selected)
    .highlight()
    .end()
  .(.open)
    .updateCount();

// bad
const   stage.selectAll().(data).enter().append(svg:svg).class(, )
    .attr(width, (radius  margin)  ).append(svg:g)
    .attr(transform, translate(  (radius  margin)    (radius  margin)  )
    .(tron.led);

// good
const   stage.selectAll()
    .(data)
  .enter().append(svg:svg)
    .classed(, )
    .attr(width, (radius  margin)  )
  .append(svg:g)
    .attr(transform, translate(  (radius  margin)    (radius  margin)  )
    .(tron.led);

  • 18.6 Leave a blank line after blocks and before the next statement.

    // bad
 (foo) {
  return bar;
}
return baz;

// good
 (foo) {
  return bar;
}

return baz;

// bad
const   {
  () {
  },
  () {
  },
};
return obj;

// good
const   {
  () {
  },

  () {
  },
};

return obj;

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Commas

  • 19.1 Leading commas: Nope.

    // bad
const story  [
    once
  , upon
  , aTime
];

// good
const story  [
  once,
  upon,
  aTime,
];

// bad
const   {
    firstName 
  , lastName Lovelace
  , birthYear 
  , superPower computers
};

// good
const   {
  firstName ,
  lastName Lovelace,
  birthYear ,
  superPower computers,
};

  • 19.2 Additional trailing comma: Yup.

    Why? This leads to cleaner git diffs. Also, transpilers like Babel will remove the additional trailing comma in the transpiled code which means you don’t have to worry about the trailing comma problem in legacy browsers.

      // bad - git diff without trailing comma
  const   {
       firstName Florence,
      lastName Nightingale
      lastName Nightingale,
      inventorOf [coxcomb graph, modern nursing]
  }

  // good - git diff with trailing comma
  const   {
       firstName Florence,
       lastName Nightingale,
      inventorOf [coxcomb chart, modern nursing],
  }

  // bad
  const   {
    firstName ,
    lastName Scully
  };

  const heroes  [
    Batman,
    Superman
  ];

  // good
  const   {
    firstName ,
    lastName Scully,
  };

  const heroes  [
    Batman,
    Superman,
  ];

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Semicolons

  • 20.1 Yup.

    // bad (function() { const Skywalker return name })() // good (() => { const Skywalker; return name; }) (); // good (guards against the function becoming an argument when two files with IIFEs are concatenated) ; (() => { const Skywalker; return name; }) ();

    Read more[8].

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Type Casting & Coercion

  • 21.1 Perform type coercion at the beginning of the statement.

  • 21.2 Strings:

    //  => this.reviewScore = 9;

// bad
const totalScore  .reviewScore  ;

// good
const totalScore  String(.reviewScore);

  • 21.3 Use parseInt for Numbers and always with a radix for type casting.

    const inputValue  ;

// bad
const    Number(inputValue);

// bad
const   inputValue;

// bad
const   inputValue >> ;

// bad
const   parseInt(inputValue);

// good
const   Number(inputValue);

// good
const   parseInt(inputValue, );

  • 21.4 If for whatever reason you are doing something wild and parseInt is your bottleneck and need to use Bitshift for performance reasons[9], leave a comment explaining why and what you’re doing.

    // good

 * parseInt was the reason my code was slow.
 * Bitshifting the String to coerce it to a
 * Number made it a lot faster.

const   inputValue >> ;

  • Note 21.5: Be careful when using bitshift operations. Numbers are represented as 64-bit values, but Bitshift operations always return a 32-bit integer (source). Bitshift can lead to unexpected behavior for integer Discussion[10]. Largest signed 32-bit Int is 2,147,483,647:

    2147483647 >>  //=> 2147483647
2147483648 >>  //=> -2147483648
2147483649 >>  //=> -2147483647

  • Booleans 21.6:

    const   ;

// bad
const hasAge   Boolean(age);

// good
const hasAge  Boolean(age);

// good
const hasAge  age;

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Naming Conventions

  • 22.1 Avoid single letter names. Be descriptive with your naming.

    // bad function () { // ... stuff... } // good function query() { // .. stuff.. }

  • 22.2 Use camelCase when Naming objects, functions, and instances

    // bad
const OBJEcttsssss  {};
const this_is_my_object  {};
function () {}

// good
const thisIsMyObject  {};
function thisIsMyFunction() {}

  • 22.3 Use PascalCase when naming constructors or classes.

    // bad
function (options) {
  .  options.;
}

const    ({
  name ,
});

// good
class  {
  constructor(options) {
    .  options.;
  }
}

const    ({
  name ,
});

  • 22.4 Use a leading underscore _ when naming private properties.

    // bad
.__firstName__  Panda;
.firstName_  Panda;

// good
._firstName  Panda;

  • 22.5 Don’t save references to this. Use arrow functions or Function#bind.

    // bad
function () {
  const   ;
  return function() {
    console(self);
  };
}

// bad
function () {
  const   ;
  return function() {
    console(that);
  };
}

// good
function () {
  return () => {
    console();
  };
}

  • 22.6 If your file exports a single class, your filename should be exactly the name of the class.

    // file contents
class CheckBox {
  // ...
}
export default CheckBox;

// in some other file
// bad
import CheckBox  ./checkBox;

// bad
import CheckBox  ./check_box;

// good
import CheckBox  ./CheckBox;

  • 22.7 Use camelCase when you export-default a function. Your filename should be identical to your function’s name.

    function makeStyleGuide() {
}

export default makeStyleGuide;

  • 22.8 Use PascalCase when you export a singleton/function library/bare Object

    const AirbnbStyleGuide  {
  es6 {
  }
};

export default AirbnbStyleGuide;

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Accessors

  • 23.1 Accessor functions for properties are not required.

  • 23.2 If you do make accessor functions use getVal() and setVal(‘hello’).

    // bad
dragon.age();

// good
dragon.getAge();

// bad
dragon.age();

// good
dragon.setAge();

  • 23.3 If the property is a boolean, use isVal() or hasVal().

    // bad
 (dragon.age()) {
  return false;
}

// good
 (dragon.hasAge()) {
  return false;
}

  • 23.4 It’s okay to create get() and set() functions, but be consistent.

    class { constructor(options = {}) { const lightsaber options.lightsaber ; .set(lightsaber, lightsaber); } (, ) { [key] val; } () { return [key]; }}

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Events

  • 24.1 When attaching data payloads to events (whether DOM events or something more proprietary like Backbone events), pass a hash instead of a raw value. This allows a subsequent contributor to add more data to the event payload without finding and updating every handler for the event. For example, instead of:

    // bad $().trigger(listingUpdated, listing.); . $().on(listingUpdated, function(, listingId) { // do something with listingId });

    prefer:

    // good $().trigger(listingUpdated, { listingId listing. }); . $().on(listingUpdated, function(, ) { // do something with data.listingId });

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jQuery

  • 25.1 jQuery Object variables with a $

    // bad
const sidebar  $(.sidebar);

// good
const $sidebar  $(.sidebar);

  • 25.2 the Cache jQuery lookups.

    // bad function setSidebar() { $(.sidebar).hide(); / /... stuff... $(.sidebar).css({ background-color }); } // good function setSidebar() { const $sidebar $(.sidebar); $sidebar.hide(); / /... stuff... $sidebar.css({ background-color }); }

  • 25.4 For DOM queries use Cascading $(‘. Sidebar ul’) or parent > child $(‘. Sidebar > ul’).jsperf [11]

  • 25.4 Use find with scoped jQuery object queries

    // bad
$(, .sidebar).hide();

// bad
$(.sidebar).().hide();

// good
$(.sidebar ul).hide();

// good
$(.sidebar > ul).hide();

// good
$sidebar.().hide();

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ECMAScript 5 Compatibility

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ECMAScript 6 Styles

  • 27.1 This is a collection of links to the various es6 features.

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Testing

  • 28.1 Yup.

    function() {
  return ;
}

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Performance

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Resources

Learning ES6

Read This

  • Annotated ECMAScript 5.1[12]

Tools

Other Style Guides

Other Styles

Further Reading

Books

Blogs

Podcasts

  • JavaScript Jabber[13]

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In the Wild

This is a list of organizations that are using this style guide. Send us a pull request or open an issue and we’ll add you to the list.

  • Aan Zee: AanZee/javascript[14]
  • Adult Swim: adult-swim/javascript[15]
  • Airbnb: airbnb/javascript[16]
  • Apartmint: apartmint/javascript[17]
  • Avalara: avalara/javascript[18]
  • Billabong: billabong/javascript[19]
  • Blendle: blendle/javascript[20]
  • Compass Learning: compasslearning/javascript-style-guide[21]
  • DailyMotion: dailymotion/javascript[22]
  • Digitpaint digitpaint/javascript[23]
  • Evernote: evernote/javascript-style-guide[24]
  • ExactTarget: ExactTarget/javascript[25]
  • Expensify Expensify/Style-Guide[26]
  • Flexberry: Flexberry/javascript-style-guide[27]
  • Gawker Media: gawkermedia/javascript[28]
  • General Electric: GeneralElectric/javascript[29]
  • GoodData: gooddata/gdc-js-style[30]
  • Grooveshark: grooveshark/javascript[31]
  • How About We: howaboutwe/javascript[32]
  • InfoJobs: InfoJobs/JavaScript-Style-Guide[33]
  • Intent Media: intentmedia/javascript[34]
  • Jam3: Jam3/Javascript-Code-Conventions[35]
  • JSSolutions: JSSolutions/javascript[36]
  • Kinetica Solutions: kinetica/javascript[37]
  • Mighty Spring: mightyspring/javascript[38]
  • MinnPost: MinnPost/javascript[39]
  • ModCloth: modcloth/javascript[40]
  • Money Advice Service: moneyadviceservice/javascript[41]
  • Muber: muber/javascript[42]
  • National Geographic: natgeo/javascript[43]
  • National Park Service: nationalparkservice/javascript[44]
  • Nimbl3: nimbl3/javascript[45]
  • Orion Health: orionhealth/javascript[46]
  • Peerby: Peerby/javascript[47]
  • Razorfish: razorfish/javascript-style-guide[48]
  • reddit: reddit/styleguide/javascript[49]
  • REI: reidev/js-style-guide[50]
  • Ripple: ripple/javascript-style-guide[51]
  • SeekingAlpha: seekingalpha/javascript-style-guide[52]
  • Shutterfly: shutterfly/javascript[53]
  • StudentSphere: studentsphere/javascript[54]
  • Target: target/javascript[55]
  • TheLadders: TheLadders/javascript[56]
  • T4R Technology: T4R-Technology/javascript[57]
  • VoxFeed: VoxFeed/javascript-style-guide[58]
  • Weggo: Weggo/javascript[59]
  • Zillow: zillow/javascript[60]
  • ZocDoc: ZocDoc/javascript[61]

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Translation

This style guide is also available in other languages:

The JavaScript Style Guide Guide

  • Reference[62]

Chat With Us About JavaScript

  • Find us on gitter[63].

Contributors

  • View Contributors[64]

License

(The MIT License)

Copyright (c) 2014 Airbnb

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the ‘Software’), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED ‘AS IS’, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

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