Array.prototype.with()

index

Zero-based index at which to change the array, converted to an integer.

• Negative index counts back from the end of the array — if start < 0, start + array.length is used.
• If start is omitted, 0 is used.
• If the index, with negative values counted backwards, is out of bounds, a RangeError is thrown.

value

Any value to be assigned to the given index.

A new array with the element at index replaced with value.

RangeError

Thrown if index > array.length or index < -array.length.

The with() method changes the value of a given index in the array, returning a new array with the element at the given index replaced with the given value. The original array is not modified. This allows you to chain array methods while doing manipulations.

The with() method never produces a sparse array. If the source array is sparse, the empty slots will be replaced with undefined in the new array.

The with() method is generic. It only expects the this value to have a length property and integer-keyed properties.

With the with() method, you can update a single element in an array and then apply other array methods.

const arr = [1, 2, 3, 4, 5];
console.log(arr.with(2, 6).map((x) => x ** 2)); // [1, 4, 36, 16, 25]

The with() method always creates a dense array.

const arr = [1, , 3, 4, , 6];
console.log(arr.with(0, 2)); // [2, undefined, 3, 4, undefined, 6]

The with() method reads the length property of this. It then reads each integer-keyed property of this and writes it to the new array, while value is written to the given index.

const arrayLike = {
  length: 3,
  unrelated: "foo",
  0: 5,
  2: 4,
};
console.log(Array.prototype.with.call(arrayLike, 0, 1));
// [ 1, undefined, 4 ]

• Polyfill of Array.prototype.with in core-js
• Array.prototype.toReversed()
• Array.prototype.toSorted()
• Array.prototype.toSpliced()
• TypedArray.prototype.with()