How to check if a string "StartsWith" another string?
How would I write the equivalent of C#'s String.StartsWith in JavaScript?
var haystack = 'hello world';
var needle = 'he';
//haystack.startsWith(needle) == true
Note: This is an old question, and as pointed out in the comments ECMAScript 2015 (ES6) introduced the .startsWith method. However, at the time of writing this update (2015) browser support is far from complete.
You can use ECMAScript 6's String.prototype.startsWith() method, but it's not yet supported in all browsers. You'll want to use a shim/polyfill to add it on browsers that don't support it. Creating an implementation that complies with all the details laid out in the spec is a little complicated, and the version defined in this answer won't do; if you want a faithful shim, use either:
String.prototype.startsWith shim, or String.prototype.startsWith . Once you've shimmed the method (or if you're only supporting browsers and JavaScript engines that already have it), you can use it like this:
"Hello World!".startsWith("He"); // true
var haystack = "Hello world";
var prefix = 'orl';
haystack.startsWith(prefix); // false
Another alternative with .lastIndexOf :
haystack.lastIndexOf(needle, 0) === 0
This looks backwards through haystack for an occurrence of needle starting from index 0 of haystack . In other words, it only checks if haystack starts with needle .
In principle, this should have performance advantages over some other approaches:
haystack . data.substring(0, input.length) === input
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