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

JavaScript has a method called String.includes() that checks whether a string contains a substring.

Use of the String.includes() method

The String.includes() method returns true if the given substring is inside the string, else it will return false.

const text = "Hello World, how are you?";

const check = text.includes("World");

console.log(check);

// Example with condition
if(check){
    console.log("Yes the substring is there.");
}

true
Yes the substring is there.

---

String.includes() method is Case Sensitive

This method is case-sensitive, which means Hello is not equal to the hello.

Now we will see how you can find the substring in a case-insensitive way. To do this we will use the String.toLowerCase() method that converts all the characters into lowercase.

const text = "Hi John";

const check1 = text.includes("john");

const subText = "joHn";
const lowerMainText = text.toLocaleLowerCase();
const lowerSubText = subText.toLowerCase();

const check2 = lowerMainText.includes(lowerSubText);

/**
 * One liner example
 * const check2 = text.toLowerCase().includes("JoHn".toLocaleLowerCase());
 */

console.log(check1);
console.log(check2);

false
true