Array.prototype.fill(value, start, end) writes one static value into some or all slots. It mutates the array in place (ES2015) and returns the same array.
array.fill(value)
array.fill(value, start)
array.fill(value, start, end)
end is exclusive (like slice)
mutates in place — returns the same array
new Array(n).fill(x) → initialize n slots
avoid fill({}) — one shared object in every slotCall array.fill. Start with this line.
array.fill(value, start=0, end=length)| Call | What it does |
|---|---|
array.fill(value, start=0, end=length) | Primary signature. |
array.fill(...) | Call with the arguments your case needs. |
Built into JavaScript. Call fill(...) on an array instance — no import required.
array.fill(value, start=0, end=length)| Parameter | Description |
|---|---|
| value | Required. Static value written into each slot |
| start | Optional. First index to fill (default 0) |
| end | Optional. Stop before this index (default length) |
| Return Value | Description |
|---|---|
| * | The same mutated array |
Overwrite indexes 1…3 with 10 (end exclusive).
const numbers = [1, 2, 3, 4, 5];
numbers.fill(10, 1, 4);
console.log(numbers); // [1, 10, 10, 10, 5]0 … 4.start=1, end=4 means write while i < 4.1, 2, 3 become 10.0 and 4 keep their original values.Reset every element with one call—no start/end needed.
const scores = [88, 92, 75, 60];
scores.fill(0);
console.log(scores); // [0, 0, 0, 0]start=0 and end=length.0.scores is mutated; no new array is created.[...scores].fill(0) to keep the original.Create n slots of the same primitive—great for buffers and placeholders.
const grid = new Array(8).fill(0);
console.log(grid);
console.log("length:", grid.length);
// Tip: for independent objects use Array.from, not fill({})
const cells = Array.from({ length: 3 }, () => ({}));
cells[0].marked = true;
console.log(cells);new Array(8) creates eight empty slots.fill(0) writes 0 into each slot safely.fill({}) would share one object—avoid it.Array.from with a factory gives a new {} per index.Array.prototype.fill() is part of ES2015 (ES6). It has been available in evergreen browsers for years and in Node.js since version 4.
Supported in Chrome 45+, Firefox 31+, Safari 9+, Edge 12+, and Node 4+. Not available in Internet Explorer.
Bottom line: Safe for essentially all modern web and Node targets. Only skip it if you must support Internet Explorer without a polyfill.
Keep only the elements that pass your test callback.
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