Starting with ECMAScript 2015, a shorter syntax for method definitions on objects initializers is introduced. It is a shorthand for a function assigned to the method's name.
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Syntax
const obj = { get property() {}, set property(value) {}, property( parametersā¦ ) {}, *generator( parametersā¦ ) {}, async property( parametersā¦ ) {}, async* generator( parametersā¦ ) {}, // with computed keys get [property]() {}, set [property](value) {}, [property]( parametersā¦ ) {}, *[generator]( parametersā¦ ) {}, async [property]( parametersā¦ ) {}, async* [generator]( parametersā¦ ) {}, };
Description
The shorthand syntax is similar to the getter and setter syntax introduced in ECMAScript 2015.
Given the following code:
const obj = { foo: function() { // ... }, bar: function() { // ... } }
You are now able to shorten this to:
const obj = { foo() { // ... }, bar() { // ... } }
Generator methods
Generator methods can be defined using the shorthand syntax as well.
When doing so:
- The asterisk (
*
) in the shorthand syntax must be before the generator property name. (That is,* g(){}
will work, butg *(){}
will not.) -
Non-generator method definitions cannot contain the
yield
keyword. This means that legacy generator functions won't work either, and will throw aSyntaxError
. Always useyield
in conjunction with the asterisk (*
).
// Using a named property const obj2 = { g: function* () { let index = 0 while (true) { yield index++ } } }; // The same object using shorthand syntax const obj2 = { * g() { let index = 0 while (true) { yield index++ } } }; const it = obj2.g() console.log(it.next().value) // 0 console.log(it.next().value) // 1
Async methods
Async methods can also be defined using the shorthand syntax.
// Using a named property const obj3 = { f: async function () { await some_promise } } // The same object using shorthand syntax const obj3 = { async f() { await some_promise } }
Async generator methods
Generator methods can also be async.
const obj4 = { f: async function* () { yield 1 yield 2 yield 3 } }; // The same object using shorthand syntax const obj4 = { async* f() { yield 1 yield 2 yield 3 } }
Method definitions are not constructable
Methods cannot be constructors! They will throw a TypeError
if you try to instantiate them.
const objA = { method() {} } new objA.method // TypeError: obj.method is not a constructor const objB = { * g() {} } new objB.g // TypeError: obj.g is not a constructor (changed in ES2016)
Examples
Simple test case
const obj = { a: 'foo', b() { return this.a } }; console.log(obj.b()) // "foo"
Computed property names
The shorthand syntax also supports computed property names.
const 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 // A global function function foo() { return 1 } let name = 'foo' console.log(window[name]()) // 1
Specifications
Specification |
---|
ECMAScript (ECMA-262) The definition of 'Method definitions' in that specification. |
Browser compatibility
Desktop | Mobile | Server | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Method definitions | Chrome Full support 39 | Edge Full support 12 | Firefox Full support 34 | IE No support No | Opera Full support 26 | Safari Full support 9 | WebView Android Full support 39 | Chrome Android Full support 39 | Firefox Android Full support 34 | Opera Android Full support 26 | Safari iOS Full support 9 | Samsung Internet Android Full support 4.0 | nodejs Full support Yes |
Async generator methods | Chrome Full support 63 | Edge Full support 79 | Firefox Full support 55 | IE No support No | Opera Full support 50 | Safari Full support 12 | WebView Android Full support 63 | Chrome Android Full support 63 | Firefox Android Full support 55 | Opera Android Full support 46 | Safari iOS Full support 12 | Samsung Internet Android Full support 8.0 | nodejs
Full support
10.0.0
|
Async methods | Chrome Full support 55 | Edge Full support 15 | Firefox Full support 52 | IE No support No | Opera Full support 42 | Safari Full support 10.1 | WebView Android Full support 55 | Chrome Android Full support 55 | Firefox Android Full support 52 | Opera Android Full support 42 | Safari iOS Full support 10.3 | Samsung Internet Android Full support 6.0 | nodejs
Full support
7.6.0
|
Generator methods are not constructable (ES2016) | Chrome Full support 42 | Edge Full support 13 | Firefox Full support 43 | IE No support No | Opera Full support 29 | Safari Full support 9.1 | WebView Android Full support 42 | Chrome Android Full support 42 | Firefox Android Full support 43 | Opera Android Full support 29 | Safari iOS Full support 9.3 | Samsung Internet Android Full support 4.0 | nodejs Full support 6.0.0 |
Legend
- Full support
- Full support
- No support
- No support
- User must explicitly enable this feature.
- User must explicitly enable this feature.