JavaScript Test if String Contains Substring

In this article, we will discuss the JavaScript Test if String Contains Substring.

Whether you are a beginner or an experienced developer, this article will provide you valuable understanding into testing strings for substrings.

Understanding JavaScript String Basics

Before we proceed into substring detection, let’s understand first the fundamental concepts:

JavaScript Strings

JavaScript strings are sequences of characters enclosed in single (‘ ‘) or double (” “) quotes. They are functional and can consists of letters, numbers, symbols, and spaces.


A substring is a smaller sequence of characters extracted from a larger string. It can be as short as one character or as long as the original string.

In the next section, we will focus on the core topic and illustrate different methods to determine if a JavaScript string consists of a specific substring.

Checking for Substrings

Method 1: Using the includes() Method

The includes() method checks if a string consists of another string and returns a Boolean value. It’s a simple and effective way to test for substrings.

const strValue = "Hi, Itsourcecode!";
const substringSample = "Itsourcecode";

if (strValue.includes(substringSample)) {
    console.log("Substring found!");
} else {
    console.log("Substring not found.");


Substring found!

Method 2: Using the indexOf() Method

The indexOf() method returns the index (position) of the first occurrence of a substring within a string. If the substring is not found, it returns -1.

Here’s an example code:

const str = "JavaScript is a functional programming language!";
const substring = "functional";

if (str.indexOf(substring) !== -1) {
    console.log("Substring found at index " + str.indexOf(substring));
} else {
    console.log("Substring not found.");


Substring found at index 16

Method 3: Using Regular Expressions (RegExp)

Regular expressions provide a powerful pattern matching capabilities. You can use them to check for substrings with complex patterns.

For example:

const str = "Welcome to JavaScript Tutorial!";
const pattern = /Tutorial/;

if (str.match(pattern)) {
    console.log("Substring found!");
} else {
    console.log("Substring not found.");


Substring found!


How do I check if a string contains multiple substrings?

You can use a combination of the methods mentioned earlier in a loop to check for multiple substrings.

Can I check for substrings in a Unicode string?

Certainly! JavaScript’s string manipulation functions work smoothly with Unicode characters.

What if I want to replace a substring with another string?

You can use the replace() method to replace a specific substring with another string.

Can I use these methods in Node.js?

Yes, these methods are available in both browsers and Node.js, making them functional for different JavaScript environments.


Mastering substring detection in JavaScript is a valuable skill for any developer. In this article, we have explored multiple methods to test if a JavaScript string consists of a substring.

By following the examples and FAQs provided, you will understand to handle substring detection tasks in your JavaScript projects.

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