String.prototype.startsWith()

The startsWith() method determines whether a string begins with the characters of another 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

The position in this string at which to begin searching for searchString; defaults to 0.

Description

This method lets you determine whether or not a string begins with another string.

Examples

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

Polyfill

This method has been added to the ECMAScript 6 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', {
    enumerable: false,
    configurable: false,
    writable: false,
    value: function (searchString, position) {
      position = position || 0;
      return this.lastIndexOf(searchString, position) === position;
    }
  });
}

Browser compatibility

See also

• String.prototype.endsWith()
• String.prototype.contains()
• String.prototype.indexOf()