How to check whether a string contains a substring in JavaScript?

ECMAScript 6 introduced String.prototype.includes:

const string = "foo";
const substring = "oo";

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

includes doesn’t have Internet Explorer support, though. In ECMAScript 5 or older environments, use String.prototype.indexOf, which returns -1 when a substring cannot be found:

var string = "foo";
var substring = "oo";

console.log(string.indexOf(substring) !== -1); // true

3 methods to check whether JavaScript String Contains substring or not. Here is a step-by-step guide.

1. includes().
2. indexOf().
3. Regular expressions (regex).

Checking if a string contains a substring is a common task in any programming language. For instance, say you are building an online game. You may want to check whether a username contains a banned phrase to make sure all usernames are suitable for your game.

1. includes().

The first method is to check if a JavaScript string contains a character or phrase using the includes() method. includes() method is the most common method for checking if a string contains a letter or series of letters, and was designed specifically for that purpose, means JavaScript string contains substring or not.

In JavaScript, includes() method determines whether a string contains the given characters within it or not. This method returns true if the string contains the characters, otherwise, it returns false. 

The syntax for the includes() method is:

string.includes(word);

Here is an example for the includes() method,

let example = "Lurem ipsum is dummy text";
let ourSubstring = "ipsum";

if (example.includes(ourSubstring)) {
	console.log("The word ipsum is in the string.");
} else {
	console.log("The word ipsum is not in the string.");
}

Note: The includes() method is case sensitive i.e, it will treat the Uppercase characters and Lowercase characters differently.

2. indexOf().

The second method is to check if a JavaScript string contains a character or phrase using the indexOf() method.

The JavaScript indexOf() method, like includes(), checks if a string includes another string. What is different is the output from these two functions.

The syntax for the indexOf() method is:

string.indexOf(word);

Here is an example for the indexOf() method,

let example = "Lurem ipsum is dummy text";
let ourSubstring = "ipsum";

if (example.indexOf(ourSubstring) != 0) {
	console.log("The word ipsum is in the string.");
} else {
	console.log("The word ipsum is not in the string.");
}

3. Using regular expression Regex.

The third and very interesting method is to check whether the javaScript string contains a substring or not.

let str = "Example String!";
/Example/.test(str);

JavaScript String Contains

There are three methods for checking if a JavaScript string contains another character or sequence of characters:

1. includes().

Syntax 

string.includes(word); // return true or false

Example

let example = "Example String!";
let ourSubstring = "Example";

if (example.includes(ourSubstring)) { // return true or false
	console.log("The word Example is in the string.");
} else {
	console.log("The word Example is not in the string.");
}

2. indexOf().

Syntax 

string.indexOf(word); // return -1

Example

let example = "Example String!";
let ourSubstring = "Example";

if (example.indexOf(ourSubstring) != 0) {
	console.log("The word Example is in the string.");
} else {
	console.log("The word Example is not in the string.");
}

3. Regular expressions (regex).

Example

let str = "Example String!";

/Example/.test(str);

we discussed the basics of strings in JavaScript. After that, we discussed three ways in which you can check if a string contains a substring in JavaScript: using includes(), indexOf(), and regex.