{{JsSidebar("Functions")}}
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 5.
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. Note that the asterisk (*) in the shorthand syntax must be before the generator property name. That is, * g(){} will work but g *(){} will not.
// 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 {{jsxref("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
| Specification | Status | Comment |
|---|---|---|
| {{SpecName('ES6', '#sec-method-definitions', 'Method definitions')}} | {{Spec2('ES6')}} | Initial definition. |
| {{SpecName('ES7', '#sec-method-definitions', 'Method definitions')}} | {{Spec2('ES7')}} | Changed that generator methods should also not have a [[Construct]] trap and will throw when used with new. |
| {{SpecName('ESDraft', '#sec-method-definitions', 'Method definitions')}} | {{Spec2('ESDraft')}} |
Browser compatibility
{{CompatibilityTable}}
| Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
|---|---|---|---|---|---|
| Method definition shorthand | {{CompatChrome("39")}} | {{CompatGeckoDesktop("34")}} | {{CompatNo}} | {{CompatOpera("26")}} | {{CompatNo}} |
| Generator methods are not constructable (ES2016) | {{CompatUnknown}} | {{CompatGeckoDesktop("43")}} | {{CompatUnknown}} | {{CompatUnknown}} | {{CompatUnknown}} |
| Feature | Android | Chrome for Android | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
|---|---|---|---|---|---|---|
| Method definition shorthand | {{CompatNo}} | {{CompatNo}} | {{CompatGeckoMobile("34")}} | {{CompatNo}} | {{CompatNo}} | {{CompatNo}} |
| Generator methods are not constructable (ES2016) | {{CompatUnknown}} | {{CompatUnknown}} | {{CompatGeckoMobile("43")}} | {{CompatUnknown}} | {{CompatUnknown}} | {{CompatUnknown}} |
SpiderMonkey-specific notes
- Prior to SpiderMonkey 38 {{geckoRelease(38)}}, "
get" and "set" were invalid names for generator methods. This has been fixed in {{bug(1073809)}}. - Prior to SpiderMonkey 41 {{geckoRelease(41)}}, curly braces were not required in method definitions. They are required from now on to conform to the ES6 specification and will throw a {{jsxref("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 {{geckoRelease(41)}}. See also {{bug(1059908)}} and {{bug(1166950)}}.