JavaScript Program to Check Whether a String Contains a Substring

Example 1: Check String with includes()

// program to check if a string contains a substring

// take input
const str = prompt('Enter a string:');
const checkString = prompt('Enter a string that you want to check:');

// check if string contains a substring
if(str.includes(checkString)) {
    console.log(`The string contains ${checkString}`);
} else {
    console.log(`The string does not contain ${checkString}`);
}

Output

Enter a string: JavaScript is fun
Enter a string that you want to check: fun
The string contains fun

The includes() method is used with the if...else statement to check whether a string contains the characters of a specified string.

Note: The includes() method is case-sensitive. Hence, fun and Fun are different.

Example 2: Check String with indexOf()

// program to check if a string contains a substring

// take input
const str = prompt('Enter a string:');
const checkString = prompt('Enter a string that you want to check:');

// check if string contains a substring
if(str.indexOf(checkString) !== -1) {
    console.log(`The string contains ${checkString}`);
} else {
    console.log(`The string does not contain ${checkString}`);
}

Output

Enter a string: JavaScript is fun
Enter a string that you want to check: fun
The string contains fun

In the above program, the indexOf() method is used with the if...else statement to check if a string contains a substring.

The indexOf() method searches a string and returns the position of the first occurrence. When a substring cannot be found, it returns -1.

Note: The indexOf() method is case sensitive.