Return TRUE if the first string starts with a specific second string JavaScript

We are required to write a JavaScript function that takes in two strings and checks whether the first string starts with the second string or not.

For example:

If the two strings are:
"Disaster management report"
"Disas"
Then our function should return true

There are multiple ways to check if a string starts with another string in JavaScript. Let's explore the most common approaches.

Using startsWith() Method (Recommended)

The startsWith() method is the built-in and most straightforward way to check if a string starts with another string:

const first = 'The game is on';
const second = 'The';

console.log(first.startsWith(second));
console.log('Disaster management report'.startsWith('Disas'));
console.log('Hello World'.startsWith('Hi'));

true
true
false

Custom Implementation Using substr()

Here's how to implement the functionality manually using substr():

const first = 'The game is on';
const second = 'The';

const startsWith = (first, second) => {
    const { length } = second;
    const sub = first.substr(0, length);
    return sub === second;
};

console.log(startsWith(first, second));
console.log(startsWith('JavaScript Tutorial', 'Java'));

true
true

Using substring() Method

Another approach using substring() method:

const checkStartsWith = (str, prefix) => {
    return str.substring(0, prefix.length) === prefix;
};

console.log(checkStartsWith('Hello World', 'Hello'));
console.log(checkStartsWith('Programming', 'Code'));

true
false

Comparison of Methods

Case-Sensitive vs Case-Insensitive

By default, all methods are case-sensitive. For case-insensitive comparison:

const str = 'Hello World';
const prefix = 'hello';

// Case-sensitive (default)
console.log(str.startsWith(prefix));

// Case-insensitive
console.log(str.toLowerCase().startsWith(prefix.toLowerCase()));

false
true

Conclusion

Use the built-in startsWith() method for modern applications as it's the most readable and efficient. For older browser support, implement a custom solution using substr() or substring().