How to know that a string starts/ends with a specific string in jQuery?

Question

One option is to use regular expressions:

if (str.match("^Hello")) {
   // do this if begins with Hello
}

if (str.match("World$")) {
   // do this if ends in world
}

For startswith, you can use indexOf:

if(str.indexOf('Hello') == 0) {

...

ref

and you can do the maths based on string length to determine 'endswith'.

if(str.lastIndexOf('Hello') == str.length - 'Hello'.length) {

There is no need of jQuery to do that. You could code a jQuery wrapper but it would be useless so you should better use

var str = "Hello World";

window.alert("Starts with Hello ? " + /^Hello/i.test(str));        

window.alert("Ends with Hello ? " + /Hello$/i.test(str));

as the match() method is deprecated.

PS : the "i" flag in RegExp is optional and stands for case insensitive (so it will also return true for "hello", "hEllo", etc.).

You do not really need jQuery for such tasks. In the ES6 specification they already have out of the box methods startsWith and endsWith.

var str = "To be, or not to be, that is the question.";
alert(str.startsWith("To be"));         // true
alert(str.startsWith("not to be"));     // false
alert(str.startsWith("not to be", 10)); // true

var str = "To be, or not to be, that is the question.";
alert( str.endsWith("question.") );  // true
alert( str.endsWith("to be") );      // false
alert( str.endsWith("to be", 19) );  // true

Currently available in FF and Chrome. For old browsers you can use their polyfills or substr

You can always extend String prototype like this:

//  Checks that string starts with the specific string
if (typeof String.prototype.startsWith != 'function') {
    String.prototype.startsWith = function (str) {
        return this.slice(0, str.length) == str;
    };
}

//  Checks that string ends with the specific string...
if (typeof String.prototype.endsWith != 'function') {
    String.prototype.endsWith = function (str) {
        return this.slice(-str.length) == str;
    };
}

And use it like this:

var str = 'Hello World';

if( str.startsWith('Hello') ) {
   // your string starts with 'Hello'
}

if( str.endsWith('World') ) {
   // your string ends with 'World'
}

ES6 now supports the startsWith() and endsWith() method for checking beginning and ending of strings. If you want to support pre-es6 engines, you might want to consider adding one of the suggested methods to the String prototype.

if (typeof String.prototype.startsWith != 'function') {
  String.prototype.startsWith = function (str) {
    return this.match(new RegExp("^" + str));
  };
}

if (typeof String.prototype.endsWith != 'function') {
  String.prototype.endsWith = function (str) {
    return this.match(new RegExp(str + "$"));
  };
}

var str = "foobar is not barfoo";
console.log(str.startsWith("foob"); // true
console.log(str.endsWith("rfoo");   // true