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(arr) {
  return arr.at(-1);
}

let invoiceRef = "myinvoice01";

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

invoiceRef = "myinvoice02";

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'

• Polyfill of String.prototype.at in core-js
• String.prototype.indexOf()
• String.prototype.lastIndexOf()
• String.prototype.charCodeAt()
• String.prototype.codePointAt()
• String.prototype.split()