Method definitions

Starting with ECMAScript 2015 (ES6), a shorter syntax for method definitions on objects initializers is introduced. It is a shorthand for a function assigned to the method's name.

Syntax

var obj = {
  property( parameters… ) {},
  *generator( parameters… ) {},
// also with computed keys:
  [property]( parameters… ) {},
  *[generator]( parameters… ) {},
// compare ES5 getter/setter syntax:
  get property() {},
  set property(value) {}
};

Description

The shorthand syntax is similar to the getter and setter syntax introduced in ECMAScript 2015.

Given the following code:

var obj = {
  foo: function() {},
  bar: function() {}
};

You are now able to shorten this to:

var obj = {
  foo() {},
  bar() {}
};

Shorthand generator methods

Generator methods can be defined using the shorthand syntax as well. When using them,

• the asterisk (*) in the shorthand syntax must be before the generator property name. That is, * g(){} will work but g *(){} will not;

• non-generator method definitions may not contain the yield keyword. This means that legacy generator functions won't work either and will throw a SyntaxError. Always use yield in conjunction with the asterisk (*).

// Using a named property (pre-ES6)
var obj2 = {
  g: function*() {
    var index = 0;
    while(true)
      yield index++;
  }
};

// The same object using shorthand syntax
var obj2 = { 
  * g() {
    var index = 0;
    while(true)
      yield index++;
  }
};

var it = obj2.g();
console.log(it.next().value); // 0
console.log(it.next().value); // 1

Method definitions are not constructable

All method definitions are not constructors and will throw a TypeError if you try to instantiate them.

var obj = { 
  method() {},
};
new obj.method; // TypeError: obj.method is not a constructor

var obj = { 
  * g() {} 
};
new obj.g; // TypeError: obj.g is not a constructor (changed in ES2016)

Examples

Simple test case

var obj = {
  a : "foo",
  b(){ return this.a; }
};
console.log(obj.b()); // "foo"

Computed property names

The shorthand syntax also supports computed property names.

var bar = {
  foo0 : function (){return 0;},
  foo1(){return 1;},
  ["foo" + 2](){return 2;},
};

console.log(bar.foo0()); // 0
console.log(bar.foo1()); // 1
console.log(bar.foo2()); // 2

Specifications

Browser compatibility

SpiderMonkey-specific notes

• Prior to SpiderMonkey 38 (Firefox 38 / Thunderbird 38 / SeaMonkey 2.35),  "get" and "set" were invalid names for generator methods. This has been fixed in bug 1073809.
• Prior to SpiderMonkey 41 (Firefox 41 / Thunderbird 41 / SeaMonkey 2.38), curly braces were not required in method definitions. They are required from now on to conform to the ES6 specification and will throw a SyntaxError in this and later versions (bug 1150855).

  var o = {x() 12}; // SyntaxError

• The restriction that only generator methods are constructors has been implemented in SpiderMonkey 41 (Firefox 41 / Thunderbird 41 / SeaMonkey 2.38). See also bug 1059908 and bug 1166950.

See also

• get
• set
• Lexical grammar