Checking Whether a String Contains a Substring

In JavaScript, you can easily check whether a string contains a substring using different methods and techniques.

Using String.includes()

The String.includes() method is a straightforward way to check if a string contains a specific substring. It returns a boolean value indicating whether the substring is found within the original string.

Example

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

console.log(sentence.includes(substring)); // Output: true

Using String.indexOf()

The String.indexOf() method can also be used to check for the presence of a substring in a string. It returns the index of the first occurrence of the substring or -1 if the substring is not found.

Example

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

console.log(sentence.indexOf(substring) !== -1); // Output: true

Using Regular Expressions

Regular expressions offer a more powerful way to check for substrings with more complex patterns.

Example

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

console.log(regex.test(sentence)); // Output: true

Case Insensitive Check

If you need to perform a case-insensitive substring check, you can use either String.toLowerCase() or the case-insensitive flag (i) with regular expressions.

Example with String.toLowerCase()

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

console.log(sentence.toLowerCase().includes(substring.toLowerCase())); // Output: true

Example with Regular Expression (case-insensitive flag)

const sentence = "The quick brown fox jumps over the lazy dog";
const regex = /fox/i;

console.log(regex.test(sentence)); // Output: true