The fill()
method fills (modifies) all the elements of an array from a start index (default zero) to an end index (default array length) with a static value. It returns the modified array.
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Syntax
arr.fill(value[, start[, end]])
Parameters
value
- Value to fill an array.
start
Optional- Start index, defaults to
0
. end
Optional- End index, defaults to
arr.length
.
Return value
The modified array.
Description
The fill
method takes up to three arguments value
, start
and end
. The start
and end
arguments are optional with default values of 0
and the length
of the array.
If start
is negative, it is treated as length+start
where length
is the length of the array. If end
is negative, it is treated as length+end
.
fill
is intentionally generic, it does not require that its this
value be an Array object.
fill
is a mutator method, it will change array itself, and return it, not just return a copy of it.
When the first parameter given to fill
is an object, it will copy the reference and fill the array with references to that object.
Examples
[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} // Objects by reference. var arr = Array(3).fill({}) // [{}, {}, {}]; arr[0].hi = "hi"; // [{ hi: "hi" }, { hi: "hi" }, { hi: "hi" }]
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 final = relativeEnd < 0 ? Math.max(len + relativeEnd, 0) : Math.min(relativeEnd, len); // Step 12. while (k < final) { 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.
Specifications
Specification | Status | Comment |
---|---|---|
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'Array.prototype.fill' in that specification. |
Standard | Initial definition. |
ECMAScript Latest Draft (ECMA-262) The definition of 'Array.prototype.fill' in that specification. |
Draft |
Browser compatibility
Desktop | Mobile | Server | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
fill | Chrome Full support 45 | Edge Full support 12 | Firefox Full support 31 | IE No support No | Opera Full support Yes | Safari Full support 8 | WebView Android Full support Yes | Chrome Android Full support 45 | Firefox Android Full support 31 | Opera Android Full support Yes | Safari iOS Full support 8 | Samsung Internet Android Full support Yes | 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.