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This is a new technology, part of the ECMAScript 2015 (ES6) standard .
This technology's specification has been finalized, but check the compatibility table for usage and implementation status in various browsers.
The keys() method returns a new Array Iterator that contains the keys for each index in the array.
Syntax
arr.keys()Examples
Basic usage
var arr = ["a", "b", "c"];
var iterator = arr.keys();
console.log(iterator.next()); // { value: 0, done: false }
console.log(iterator.next()); // { value: 1, done: false }
console.log(iterator.next()); // { value: 2, done: false }
console.log(iterator.next()); // { value: undefined, done: true }
Key iterator doesn't ignore holes
var arr = ["a", , "c"]; var sparseKeys = Object.keys(arr); var denseKeys = [...arr.keys()]; console.log(sparseKeys); // ['0', '2'] console.log(denseKeys); // [0, 1, 2]
Specifications
| Specification | Status | Comment |
|---|---|---|
| ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'Array.prototype.keys' in that specification. |
Standard | Initial definition. |
Browser compatibility
| Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
|---|---|---|---|---|---|
| Basic support | 38 | 28 (28) | Not supported | 25 | 7.1 |
| Feature | Android | Chrome for Android | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
|---|---|---|---|---|---|---|
| Basic support | Not supported | Not supported | 28.0 (28) | Not supported | Not supported | 8.0 |