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String.prototype.codePointAt()

The codePointAt() method returns a non-negative integer that is the Unicode code point value.

Syntax

str.codePointAt(pos)

Parameters

pos
Position of an element in the String to return the code point value from.

Return value

A number representing the code unit value of the character at the given index; undefined if there is no element at pos.

Description

If there is no element at the specified position, undefined is returned. If no UTF-16 surrogate pair begins at pos, the code unit at pos is returned.

Examples

Using codePointAt()

'ABC'.codePointAt(1);          // 66
'\uD800\uDC00'.codePointAt(0); // 65536

'XYZ'.codePointAt(42); // undefined

Polyfill

The following extends Strings to include the codePointAt() function as specified in ECMAScript 6 for browsers not supporting it natively.

/*! http://mths.be/codepointat v0.1.0 by @mathias */
if (!String.prototype.codePointAt) {
  (function() {
    'use strict'; // needed to support `apply`/`call` with `undefined`/`null`
    var codePointAt = function(position) {
      if (this == null) {
        throw TypeError();
      }
      var string = String(this);
      var size = string.length;
      // `ToInteger`
      var index = position ? Number(position) : 0;
      if (index != index) { // better `isNaN`
        index = 0;
      }
      // Account for out-of-bounds indices:
      if (index < 0 || index >= size) {
        return undefined;
      }
      // Get the first code unit
      var first = string.charCodeAt(index);
      var second;
      if ( // check if it’s the start of a surrogate pair
        first >= 0xD800 && first <= 0xDBFF && // high surrogate
        size > index + 1 // there is a next code unit
      ) {
        second = string.charCodeAt(index + 1);
        if (second >= 0xDC00 && second <= 0xDFFF) { // low surrogate
          // http://mathiasbynens.be/notes/javascript-encoding#surrogate-formulae
          return (first - 0xD800) * 0x400 + second - 0xDC00 + 0x10000;
        }
      }
      return first;
    };
    if (Object.defineProperty) {
      Object.defineProperty(String.prototype, 'codePointAt', {
        'value': codePointAt,
        'configurable': true,
        'writable': true
      });
    } else {
      String.prototype.codePointAt = codePointAt;
    }
  }());
}

Specifications

Specification Status Comment
ECMAScript 2015 (6th Edition, ECMA-262)
The definition of 'String.prototype.codePointAt' in that specification.
Standard Initial definition.
ECMAScript 2017 Draft (ECMA-262)
The definition of 'String.prototype.codePointAt' in that specification.
Draft  

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support 41 29 (29) 11 28 No support
Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support No support No support 29.0 (29) No support No support No support

See also

Document Tags and Contributors

 Contributors to this page: eduardoboucas, metamatt, fscholz, fasttime, ziyunfei, Mingun, trueorfalse
 Last updated by: eduardoboucas,