The keys()
method returns a new Array Iterator
that contains the keys for each index in the array.
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 }
Syntax
arr.keys()
Return value
A new Array
iterator object.
Examples
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. |
ECMAScript Latest Draft (ECMA-262) The definition of 'Array.prototype.keys' in that specification. |
Draft |
Browser compatibility
See also
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erikadoyle,
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Last updated by:
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