How Can I Check for a Substring in a JavaScript String?

Checking for Substring Presence in a JavaScript String

Despite the absence of an explicit String.contains() method in JavaScript, there are various approaches to determine if a string includes a specific substring.

One widely-used method is the String.indexOf() function. This function returns the index of the first occurrence of a specified substring within a string. If the substring is not found, it returns -1.

const string = "Hello world!";
const substring = "world";

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

ES6 introduced the String.prototype.includes() method, providing a more concise syntax for this check. It returns a boolean value indicating whether the string includes the specified substring.

const string = "Hello world!";
const substring = "world";

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

Using regular expressions is another option. The String.match() method takes a regular expression as an argument and returns an array of matches. If the substring is found, the resulting array will have a length greater than 0.

const string = "Hello world!";
const substring = "world";
const regex = new RegExp(substring);

const matches = string.match(regex);
if (matches && matches.length > 0) {
  console.log("Substring found!");
} else {
  console.log("Substring not found.");
}

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