W3cubDocs

/JavaScript

string.startsWith

The startsWith() method determines whether a string begins with the characters of a specified string, returning true or false as appropriate.

Syntax

str.startsWith(searchString[, position])

Parameters

searchString
The characters to be searched for at the start of this string.
position Optional
The position in this string at which to begin searching for searchString. Defaults to 0.

Return value

true if the given characters are found at the beginning of the string; otherwise, false.

Description

This method lets you determine whether or not a string begins with another string. This method is case-sensitive.

Polyfill

This method has been added to the ECMAScript 2015 specification and may not be available in all JavaScript implementations yet. However, you can polyfill String.prototype.startsWith() with the following snippet:

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;
        }
    });
}

A more robust (fully ES2015 specification compliant), but less performant and compact, Polyfill is available on GitHub by Mathias Bynens.

Examples

Using startsWith()

//startswith
let str = 'To be, or not to be, that is the question.'

console.log(str.startsWith('To be'))          // true
console.log(str.startsWith('not to be'))      // false
console.log(str.startsWith('not to be', 10))  // true

Specifications

Browser compatibilityUpdate compatibility data on GitHub

Desktop
Chrome Edge Firefox Internet Explorer Opera Safari
startsWith 41 12 17 No 28 9
Mobile
Android webview Chrome for Android Firefox for Android Opera for Android Safari on iOS Samsung Internet
startsWith ≤37 36 17 24 9 3.0
Server
Node.js
startsWith 4.0.0
4.0.0
0.12
Disabled
Disabled From version 0.12: this feature is behind the --harmony runtime flag.

See also

© 2005–2018 Mozilla Developer Network and individual contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://wiki.developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/startsWith