Below are a range of useful string operations available in JavaScript

Table of Contents

• Basic Operations
  • Concatenation
  • Length
• Finding and Extracting
  • indexOf
  • lastIndexOf
  • slice
  • substring
  • substr (Deprecated)
• Comparison
  • localeCompare
• Transformation
  • toLowerCase
  • toUpperCase
  • trim
• Matching
  • match
  • matchAll
  • startsWith
  • endsWith
  • includes
• Replacement
  • replace
  • replaceAll
• Splitting
  • split

Basic Operations

Concatenation

Combine two or more strings.

let greeting = "Hello, ";
let name = "World!";
console.log(greeting + name); // "Hello, World!"

Length

Find out how many characters are in a string

let text = "Hello, World!";
console.log(text.length); // 13

Finding and Extracting

IndexOf

Find the first index number for a substring

let text = "Hello, World!";
console.log(text.indexOf("World")); // 7

LastIndexOf

Find the last index number for a substring

let text = "Hello, World, Hello!";
console.log(text.lastIndexOf("Hello")); // 13

Slice

Extracts a section of a string from startIndex to, but not including, endIndex. If endIndex is not provided, it extracts till the end of the string. If endIndex is negative, it’s treated as strLength + endIndex where strLength is the string’s length.

let text = "Hello, World!";
console.log(text.slice(7, 12)); // "World"

Substring

Extracts characters from startIndex up to, but not including, endIndex. If endIndex is not specified, extraction goes to the end of the string. Unlike slice(), if endIndex is less than startIndex, substring will swap the two arguments; slice will not.

let text = "Hello, World!";
console.log(text.substring(7, 12)); // "World"

Comparison

localeCompare

Compares two strings in the current locale.

console.log("a".localeCompare("b")); // -1
console.log("a".localeCompare("a")); // 0
console.log("b".localeCompare("a")); // 1

Transform

toLowerCase

Converts a string to lowercase letters.

let text = "Hello, World!";
console.log(text.toLowerCase()); // "hello, world!"

toUpperCase

Converts a string to uppercase letters.

let text = "Hello, World!";
console.log(text.toUpperCase()); // "HELLO, WORLD!"

Trim

let text = "   Hello, World!   ";
console.log(text.trim()); // "Hello, World!"

Matching

Match

Retrieves the result of matching a string against a regular expression.

let text = "The rain in SPAIN stays mainly in the plain";
console.log(text.match(/ain/g)); // ["ain", "ain", "ain"]

MatchAll

Returns an iterator of all results matching a string against a regular expression.

let text = "The rain in SPAIN stays mainly in the plain";
let regex = /ain/g;
console.log(Array.from(text.matchAll(regex))); // [Array with matches]

StartsWith

Determines whether a string begins with the characters of a specified string.

let text = "Hello, World!";
console.log(text.startsWith("Hello")); // true

EndsWith

Determines whether a string ends with the characters of a specified string.

let text = "Hello, World!";
console.log(text.endsWith("World!")); // true

Includes

Determines whether one string may be found within another string.

let text = "Hello, World!";
console.log(text.includes("World")); // true

Replacement

Replace

Replaces occurrences of a substring with another substring in a string.

let text = "Hello, World!";
console.log(text.replace("World", "JavaScript")); // "Hello, JavaScript!"

ReplaceAll

Replaces all occurrences of a substring with another substring in a string.

let text = "Hello, World! World is great.";
console.log(text.replaceAll("World", "JavaScript")); // "Hello, JavaScript! JavaScript is great."

Splitting

Split

Splits a string into an array of substrings based on a specified separator.

let text = "Hello, World! How are you?";
console.log(text.split(" ")); // ["Hello,", "World!", "How", "are", "you?"]
console.log(text.split(", ")); // ["Hello", "World! How are you?"]
console.log(text.split("")); // Splits every character into an array