Array.prototype.at

The at() method takes an integer value and returns the item at that index, allowing for positive and negative integers. Negative integers count back from the last item in the array.

Syntax

at(index)

Parameters

• index
  • : Zero-based index of the array element to be returned, converted to an integer. Negative index counts back from the end of the array — if index < 0, index + array.length is accessed.

Return value

The element in the array matching the given index. Always returns undefined if index < -array.length or index >= array.length without attempting to access the corresponding property.

Description

The at() method is equivalent to the bracket notation when index is non-negative. For example, array[0] and array.at(0) both return the first item. However, when counting elements from the end of the array, you cannot use array[-1] like you may in Python or R, because all values inside the square brackets are treated literally as string properties, so you will end up reading array["-1"], which is just a normal string property instead of an array index.

The usual practice is to access Array.prototype.length and calculate the index from that — for example, array[array.length - 1]. The at() method allows relative indexing, so this can be shortened to array.at(-1).

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