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String.prototype.at() - JavaScript | MDN

Baseline Widely available

The at() method of String values takes an integer value and returns a new String consisting of the single UTF-16 code unit located at the specified offset. This method allows for positive and negative integers. Negative integers count back from the last string character.

const sentence = "The quick brown fox jumps over the lazy dog.";

let index = 5;

console.log(`An index of ${index} returns the character ${sentence.at(index)}`);
// Expected output: "An index of 5 returns the character u"

index = -4;

console.log(`An index of ${index} returns the character ${sentence.at(index)}`);
// Expected output: "An index of -4 returns the character d"

index

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

A String consisting of the single UTF-16 code unit located at the specified position. Returns undefined if the given index can not be found.

The following example provides a function which returns the last character found in a specified string.

// A function which returns the last character of a given string
function returnLast(str) {
  return str.at(-1);
}

let invoiceRef = "my-invoice01";

console.log(returnLast(invoiceRef)); // '1'

invoiceRef = "my-invoice02";

console.log(returnLast(invoiceRef)); // '2'

Here we compare different ways to select the penultimate (last but one) character of a String. Whilst all below methods are valid, it highlights the succinctness and readability of the at() method.

const myString = "Every green bus drives fast.";

// Using length property and charAt() method
const lengthWay = myString.charAt(myString.length - 2);
console.log(lengthWay); // 't'

// Using slice() method
const sliceWay = myString.slice(-2, -1);
console.log(sliceWay); // 't'

// Using at() method
const atWay = myString.at(-2);
console.log(atWay); // 't'

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