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const str = 'Hello, World!';
console.log(str.startsWith('Hello'));  // true
console.log(str.startsWith('World'));  // false

If you've ever had to check if a string starts with a certain substring in JavaScript, you know how much of a pain it can be without the right tools. That's where the `startsWith` method comes in – a game-changer for string manipulation. I honestly prefer using this method over others because of its simplicity and readability.

What is JavaScript startsWith?

The `startsWith` method is a part of the String prototype in JavaScript, which means you can call it on any string value. It checks if the string starts with the specified substring and returns a boolean value – `true` if it does, and `false` otherwise.

Syntax

The syntax for `startsWith` is straightforward:

str.startsWith(searchString[, position])

Where `searchString` is the substring you're looking for, and `position` is an optional parameter that specifies the position to start searching from (default is 0).

Examples

Basic usage

const str = 'JavaScript is awesome!';
console.log(str.startsWith('JavaScript'));  // true
console.log(str.startsWith('Java'));  // true
console.log(str.startsWith('Script'));  // false

Using the position parameter

const str = 'JavaScript is awesome!';
console.log(str.startsWith('is', 11));  // true
console.log(str.startsWith('is', 10));  // false

Case sensitivity

const str = 'JavaScript is awesome!';
console.log(str.startsWith('javascript'));  // false
console.log(str.toLowerCase().startsWith('javascript'));  // true

Non-string values

const str = '123';
console.log(str.startsWith(1));  // true
console.log(str.startsWith([1]));  // false

Polyfill for older browsers

If you need to support older browsers that don't have the `startsWith` method, you can use a polyfill:

if (!String.prototype.startsWith) {
    Object.defineProperty(String.prototype, 'startsWith', {
        value: function(search, rawPos) {
            var pos = rawPos > 0 ? rawPos|0 : 0;
            return this.substring(pos, pos + search.length) === search;
        }
    });
}

TypeScript support

The `startsWith` method is also available in TypeScript, with the same syntax and usage as in JavaScript.

Conclusion

In conclusion, the `javascript startsWith` method is a powerful tool for string manipulation in JavaScript. Its simplicity and readability make it a great choice for many use cases. So next time you need to check if a string starts with a certain substring, don't hesitate to use this method.

And if you need to convert your code from one language to another — say, from JavaScript to TypeScript or Python — be sure to check out CodeConverter.co, an AI-powered code language converter that can save you hours of tedious work.