The fill()
method changes all elements in an array to a static value, from a start index (default 0
) to an end index (default array.length
). It returns the modified array.
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Syntax
arr.fill(value[, start[, end]])
Parameters
value
- Value to fill the array with. (Note all elements in the array will be this exact value.)
start
Optional- Start index, default
0
. end
Optional- End index, default
arr.length
.
Return value
The modified array, filled with value
.
Description
- If
start
is negative, it is treated asarray.length + start
. - If
end
is negative, it is treated asarray.length + end
. fill
is intentionally generic: it does not require that itsthis
value be anArray
object.fill
is a mutator method: it will change the array itself and return it, not a copy of it.- If the first parameter is an object, each slot in the array will reference that object.
Polyfill
if (!Array.prototype.fill) { Object.defineProperty(Array.prototype, 'fill', { value: function(value) { // Steps 1-2. if (this == null) { throw new TypeError('this is null or not defined'); } var O = Object(this); // Steps 3-5. var len = O.length >>> 0; // Steps 6-7. var start = arguments[1]; var relativeStart = start >> 0; // Step 8. var k = relativeStart < 0 ? Math.max(len + relativeStart, 0) : Math.min(relativeStart, len); // Steps 9-10. var end = arguments[2]; var relativeEnd = end === undefined ? len : end >> 0; // Step 11. var finalValue = relativeEnd < 0 ? Math.max(len + relativeEnd, 0) : Math.min(relativeEnd, len); // Step 12. while (k < finalValue) { O[k] = value; k++; } // Step 13. return O; } }); }
If you need to support truly obsolete JavaScript engines that don't support Object.defineProperty
, it's best not to polyfill Array.prototype
methods at all, as you can't make them non-enumerable.
Examples
Using fill
[1, 2, 3].fill(4) // [4, 4, 4] [1, 2, 3].fill(4, 1) // [1, 4, 4] [1, 2, 3].fill(4, 1, 2) // [1, 4, 3] [1, 2, 3].fill(4, 1, 1) // [1, 2, 3] [1, 2, 3].fill(4, 3, 3) // [1, 2, 3] [1, 2, 3].fill(4, -3, -2) // [4, 2, 3] [1, 2, 3].fill(4, NaN, NaN) // [1, 2, 3] [1, 2, 3].fill(4, 3, 5) // [1, 2, 3] Array(3).fill(4) // [4, 4, 4] [].fill.call({ length: 3 }, 4) // {0: 4, 1: 4, 2: 4, length: 3} // A single object, referenced by each slot of the array: let arr = Array(3).fill({}) // [{}, {}, {}] arr[0].hi = "hi" // [{ hi: "hi" }, { hi: "hi" }, { hi: "hi" }]
Specifications
Specification |
---|
ECMAScript (ECMA-262) The definition of 'Array.prototype.fill' in that specification. |
Browser compatibility
The compatibility table in this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.
Desktop | Mobile | Server | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
fill | Chrome Full support 45 | Edge Full support 12 | Firefox Full support 31 | IE No support No | Opera Full support 32 | Safari Full support 8 | WebView Android Full support 45 | Chrome Android Full support 45 | Firefox Android Full support 31 | Opera Android Full support 32 | Safari iOS Full support 8 | Samsung Internet Android Full support 5.0 | nodejs
Full support
4.0.0
|
Legend
- Full support
- Full support
- No support
- No support
- User must explicitly enable this feature.
- User must explicitly enable this feature.