The startsWith()
method determines whether a string begins with the characters of a specified string, returning true
or false
as appropriate.
str.startsWith(searchString[, position])
searchString
position
Optional
searchString
. Defaults to 0
.true
if the given characters are found at the beginning of the string; otherwise, false
.
This method lets you determine whether or not a string begins with another string. This method is case-sensitive.
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.
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
Specification |
---|
ECMAScript (ECMA-262) The definition of 'String.prototype.startsWith' in that specification. |
Desktop | ||||||
---|---|---|---|---|---|---|
startsWith |
41 | 12 | 17 | No | 28 | 9 |
Mobile | ||||||
---|---|---|---|---|---|---|
startsWith |
≤37 | 36 | 17 | 24 | 9 | 3.0 |
Server | |
---|---|
startsWith |
4.0.0
|
String.prototype.endsWith()
String.prototype.includes()
String.prototype.indexOf()
String.prototype.lastIndexOf()
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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