How to Check Whether a String Contains a Substring in JavaScript?

Valerie M.

—October 21, 2022

The Problem

You want to check whether a string contains a substring in JavaScript. What are the different ways to do this?

The Solution

There are a number of ways you could approach this problem. We’ll take a look at two methods: includes() and indexOf().

The includes() method

You can use JavaScript’s includes() method to check whether a string contains a substring. This will return true if the substring is found, or false if not.

Consider the code example below:

const str = 'This is my example string!';
const substr = 'my';

console.log(str.includes(substr));

The above code would output true.

Note that includes() performs a case-sensitive search. To work around this, you can convert the string to lower case using toLowerCase() as follows:

console.log(str.toLowerCase().includes(substr));

Furthermore, a position can also be passed as an argument to specify the position at which to begin searching the string for the substring. The default position is 0. If you want to begin searching at position 2, you would write:

console.log(str.includes(substr, 2));

The indexOf() method

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

const str = 'This is my example string!';
const substr = 'my';

console.log(str.indexOf(substr));

The code above returns 8.

You can also include the position at which to begin searching the string for the substring. The default position is 0.

Other search methods you can consider include:

• search(regExp) – Returns the index of the first match between regExp and the string. If no match is found, -1 is returned.
• lastIndexOf(searchValue) – Returns the index position of the last occurrence of searchValue inside a string.
• match(searchValue) – Finds the searchValue, a regular expression, within a given string and returns an array containing the matches.
• charAt(index) – Returns a string representing the character at the specified index. If the index is out of range, it returns an empty string.
• startsWith(searchValue) – Returns true or false if searchValue is found at the beginning of a string.
• endsWith(searchValue) – Returns true or false if a string ends with the searchValue.

Further Reading

If you’re looking to get a deeper understanding of how JavaScript application monitoring works, take a look at the following articles:

• Making your JavaScript projects less noisy
• 3 Ways to Improve JavaScript Applications
• JavaScript Debugging Hub
• Sentry for JavaScript
• JavaScript Error and Performance Monitoring
• 11 Habits of Highly Effective Developers