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 substring is contained in a javascript string, e.g. myString.includes('substring'). The String.includes method returns true if the substring is contained in the string and false otherwise.

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// Not Supported in IE 6-11
const string = 'hello world';
const substring = 'hello';

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

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

In the example, we've invoked the String.includes method with a substring.

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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// Supported in IE 6-10
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
}

In the code snippet, the substring is contained in the string, starting at index 0, therefore the indexOf method returns 0.

The code block of our if conditional check does not run if String.indexOf returns -1, which happens when the substring is not contained in the string.

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