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 Optional

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

Return value

true if the string begins with the characters of the search 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 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) {
    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

Browser compatibility

See also

• String.prototype.endsWith()
• String.prototype.includes()
• String.prototype.indexOf()
• String.prototype.lastIndexOf()