Baseline 2023
Newly available
The toReversed() method of Array instances is the copying counterpart of the reverse() method. It returns a new array with the elements in reversed order.
None.
Return valueA new array containing the elements in reversed order.
DescriptionThe toReversed() method transposes the elements of the calling array object in reverse order and returns a new array.
When used on sparse arrays, the toReversed() method iterates empty slots as if they have the value undefined.
The toReversed() method is generic. It only expects the this value to have a length property and integer-keyed properties.
The following example creates an array items, containing three elements, then creates a new array that's the reverse of items. The items array remains unchanged.
const items = [1, 2, 3];
console.log(items); // [1, 2, 3]
const reversedItems = items.toReversed();
console.log(reversedItems); // [3, 2, 1]
console.log(items); // [1, 2, 3]
The return value of toReversed() is never sparse. Empty slots become undefined in the returned array.
console.log([1, , 3].toReversed()); // [3, undefined, 1]
console.log([1, , 3, 4].toReversed()); // [4, 3, undefined, 1]
The toReversed() method reads the length property of this. It then visits each property having an integer key between length - 1 and 0 in descending order, adding the value of the current property to the end of the array to be returned.
const arrayLike = {
length: 3,
unrelated: "foo",
2: 4,
};
console.log(Array.prototype.toReversed.call(arrayLike));
// [4, undefined, undefined]
// The '0' and '1' indices are not present so they become undefined
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