startsWith method

ES6 introduces the startsWith method to the String object, it checks whether or not a string starts with certain characters.

In ES5 we can use the indexOf method which works fine. It’s just not very clear at first glance what it does.

const lipsum = 'lorem ipsum dolor sit amet';
const check = lipsum.indexOf('l') === 0;

// true
console.log(check);

startsWith does exactly the same, but looks a lot cleaner and is much easier to read. Even if you’re not an experienced developer, its pretty clear what this code does.

const lipsum = 'lorem ipsum dolor sit amet';
const check = lipsum.startsWith('l');

// true
console.log(check);

The params

Nice and simple, there’s just the two:

• searchValue – the string you want to search for
• startPosition– the index to start at (optional)

searchValue

The first parameter can be a single character or a longer string.

const lipsum = 'lorem ipsum dolor sit amet';

// true
lipsum.startsWith('l');
lipsum.startsWith('lored ipsum');

// false
lipsum.startsWith('i');

If searchValue is longer than the string itself, it will return false.

// false
lipsum.startsWith('lorem ipsum dolor sit amet, consectetur');

It’s also case sensitive, it must exactly match to return true.

// false
lipsum.startsWith('Lorem');

startPosition

By default it’ll start at the first character (position 0 since JavaScript is zero-indexed). We can override this by passing a second parameter.

In this example we’ll run the check against the second character.

// true
lipsum.startsWith('o', 1);