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.

This is not to suggest there is anything wrong with using the square bracket notation. For example array[0] would return the first item. However instead of using array.length for latter items; e.g. array[array.length-1] for the last item, you can call array.at(-1). (See the examples below)

index

The index (position) of the array element to be returned. Supports relative indexing from the end of the array when passed a negative index; i.e. if a negative number is used, the element returned will be found by counting back from the end of the array.

The element in the array matching the given index. Returns undefined if the given index can not be found.

The following example provides a function which returns the last element found in a specified array.

// Our array with items
const cart = ['apple', 'banana', 'pear'];

// A function which returns the last item of a given array
function returnLast(arr) {
  return arr.at(-1);
}

// Get the last item of our array 'cart'
const item1 = returnLast(cart);
console.log(item1); // Logs: 'pear'

// Add an item to our 'cart' array
cart.push('orange');
const item2 = returnLast(cart);
console.log(item2); // Logs: 'orange'

This example compares different ways to select the penultimate (last but one) item of an Array. While all the methods shown below are valid, this example highlights the succinctness and readability of the at() method.

// Our array with items
const colors = ['red', 'green', 'blue'];

// Using length property
const lengthWay = colors[colors.length-2];
console.log(lengthWay); // Logs: 'green'

// Using slice() method. Note an array is returned
const sliceWay = colors.slice(-2, -1);
console.log(sliceWay[0]); // Logs: 'green'

// Using at() method
const atWay = colors.at(-2);
console.log(atWay); // Logs: 'green'

• Polyfill of Array.prototype.at in core-js
• A polyfill for the at() method.
• Array.prototype.find() – return a value based on a given test.
• Array.prototype.includes() – test whether a value exists in the array.
• Array.prototype.indexOf() – return the index of a given element.