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Table of Contents
1. includes() method (Recommended for simple checks)
2. indexOf() method
3. Using search() with regular expressions
4. Using regular expressions with test()
Home Web Front-end JS Tutorial How do you check if a string contains a substring in JavaScript?

How do you check if a string contains a substring in JavaScript?

Aug 02, 2025 am 02:09 AM
string

Use include() method to directly determine whether a string contains a substring, return true or false, which is recommended for simple checking; 2. The indexOf() method returns the index value or -1, and needs to be used in conjunction with the use of not equal to -1; 3. The search() method supports regular expressions, suitable for scenarios that require regular matching, but only returns the first matching position; 4. The test() method is suitable for complex pattern matching, with high flexibility but too complex for simple requirements; in summary, for ordinary substring searches, include() is the clearest and efficient choice, while regular related methods are suitable for situations where pattern matching is required. In the end, it is recommended to use include() method to complete basic inclusion checks first.

How do you check if a string contains a substring in JavaScript?

You can check if a string contains a substring in JavaScript using several methods. Here are the most common and practical ones:

How do you check if a string contains a substring in JavaScript?

The includes() method is the most straightforward and readable way to check for a substring. It returns true if the substring is found, and false otherwise.

 const str = "Hello, world!";
console.log(str.includes("world")); // true
console.log(str.includes("JavaScript")); // false

It's case-sensitive, so:

How do you check if a string contains a substring in JavaScript?
 console.log(str.includes("World")); // false

If you need case-insensitive search, convert both strings to lowercase:

 const searchString = "WORLD";
console.log(str.toLowerCase().includes(searchString.toLowerCase())); // true

2. indexOf() method

This method returns the index of the first occurrence of the substring, or -1 if not found. You can use it in a boolean context.

How do you check if a string contains a substring in JavaScript?
 const str = "Hello, world!";
console.log(str.indexOf("world") !== -1); // true
console.log(str.indexOf("JavaScript") !== -1); // false

Like includes() , it's also case-sensitive.

3. Using search() with regular expressions

The search() method takes a regular expression and returns the index of the match, or -1 if not found.

 const str = "Hello, world!";
console.log(str.search("world") !== -1); // true

It's useful when you want to use regex patterns:

 // Case-insensitive search using regex
console.log(str.search(/WORLD/i) !== -1); // true

But note: search() doesn't support global flags like g , and it always returns the first match.

4. Using regular expressions with test()

For more complex pattern matching, you can use RegExp.prototype.test() .

 const str = "Hello, world!";
const regex = /world/;
console.log(regex.test(str)); // true

This is powerful when you need pattern matching (eg, word boundaries, wildcards), but overkill for simple substring checks.


Quick comparison:

Method Case-sensitive Regex support Easy to use?
includes() Yes No ? Yes
indexOf() Yes No ? Yes
search() Yes (unless i flag) Yes ?? Medium
test() Depends on regex Yes ?? Medium

For most cases, use includes() — it's clean, readable, and built for this exact purpose. Use regex-based methods only when you need pattern matching.

Basically, if you're just checking whether one string is inside another, includes() is your best bet.

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