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.
Examples
Using startsWith()
//startswith var 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
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) { String.prototype.startsWith = function(searchString, position){ position = position || 0; return this.substr(position, searchString.length) === searchString; }; }
A more robust and optimized Polyfill is available on GitHub by Mathias Bynens.
Specifications
Specification | Status | Comment |
---|---|---|
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'String.prototype.startsWith' in that specification. |
Standard | Initial definition. |
ECMAScript Latest Draft (ECMA-262) The definition of 'String.prototype.startsWith' in that specification. |
Draft |
Browser compatibility
Feature | Chrome | Firefox (Gecko) | Edge | Internet Explorer | Opera | Safari |
---|---|---|---|---|---|---|
Basic support | 41 | 17 (17) | (Yes) | No support | 28 | 9 |
Feature | Android | Chrome for Android | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
---|---|---|---|---|---|---|
Basic support | No support | 36 | 17.0 (17) | No support | No support | 9 |
Please note that although the MSDN documentation for this method (https://msdn.microsoft.com/en-us/library/mt146831(v=vs.94).aspx) clearly indicates that it is not supported in Internet Explorer, the method does seem to work, as far back as Internet Explorer 8.