Array.prototype.with(index, value) returns a new array with the element at index replaced by value. The original array stays unchanged. Negative indexes count from the end—like at().
array.with(index, value) → new array (original untouched)
with(2, "pineapple") → replace index 2
with(-1, "z") → replace last element
arr[i] = x → mutates in place
arr.with(i, x) → new copy
out of range → RangeError (does not grow the array)Call array.with. Start with this line.
array.with(index, value)| Call | What it does |
|---|---|
array.with(index, value) | Primary signature. |
array.with(...) | Call with the arguments your case needs. |
Built into JavaScript. Call with(...) on an array instance — no import required.
array.with(index, value)| Parameter | Description |
|---|---|
| index | Required. Position to replace (negative OK) |
| value | Required. New element at that index |
| Return Value | Description |
|---|---|
| * | New array (shallow copy + one change) |
Swap one element and keep a new array.
const fruits = ["apple", "orange", "banana", "grape"];
const updated = fruits.with(2, "pineapple");
console.log(updated);
console.log(fruits[2]); // still "banana""banana".fruits[2] is still "banana".Prove identity and contents differ after with().
const original = [1, 2, 3, 4, 5];
const modified = original.with(2, 999);
console.log(original);
console.log(modified);
console.log(original === modified); // false999 there.3; modified has 999.=== is false—safe for immutable state updates.Replace the last element with with(-1, …).
const items = ["a", "b", "c"];
console.log(items.with(-1, "z"));at(-1)."c" becomes "z" in the copy.items is still ["a","b","c"].Array.prototype.with() was added in ES2023 with the other immutable array helpers (toReversed, toSorted, toSpliced).
Supported in Chrome 110+, Firefox 115+, Safari 16+, Edge 110+, and Node.js 20+. Not available in Internet Explorer or very old browsers.
Bottom line: For older targets, feature-detect with if ("with" in Array.prototype) or fall back to [...arr.slice(0, i), val, ...arr.slice(i + 1)].
Explore more helpers—from map and filter to the ES2023 copy methods.
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