Check if a String contains a Substring in JavaScript

Check if a String contains a Substring with String.includes #

Use the String.includes() method to check if a string contains a substring, e.g. myString.includes('substring'). The String.includes method returns true if the substring is contained in the string, otherwise false is returned.

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const string = 'hello world';
const substring = 'hello';

console.log(string.includes(substring)); // 👉️ true

if (string.includes(substring)) {
  // 👉️ substring is contained in string
}

We used the String.includes method to check if a substring is contained in a string.

If the substring is contained in the string, the String.includes method returns true, otherwise it returns false.

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const string = 'HELLO world';
const substring = 'hello';

// 👇️ true
console.log(
  string.toLowerCase().includes(substring.toLowerCase())
);

if (string.toLowerCase().includes(substring.toLowerCase())) {
  // 👉️ substring is contained in string
}

Check if a String contains a Substring with String.indexOf #

To check if a substring is contained in a JavaScript string:

1. Call the indexOf method on the string, passing it the substring as a parameter - string.indexOf(substring)
2. Conditionally check if the returned value is not equal to -1
3. If the returned value is not equal to -1, the string contains the substring

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const string = 'hello world';
const substring = 'hello';

const index = string.indexOf(substring);
console.log(index); // 👉️ 0

if (string.indexOf(substring) !== -1) {
  // 👉️ substring is contained in string
}

The substring in the code sample is contained in the string starting at index 0. Therefore the indexOf method returns 0.

Our if block is only run if the String.indexOf method didn't return -1. The method only returns -1 if the substring is not contained in the string.

Which approach you pick is a matter of personal preference. I'd use the String.includes() method as it is easier to read and more direct.

Further Reading #

• Check if Array of Strings contains a Substring in JS
• Replace a String case insensitive in JavaScript
• Check if String contains specific Character in JavaScript
• Split a String only on the First Occurrence of a Character
• Get the first N characters of a String in JavaScript
• Get the last N characters of a String in JavaScript
• Extract a Number from a String in JavaScript
• Get the first N words from a String in JavaScript
• How to check if a String is Empty in JavaScript