String.prototype.codePointAt()

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

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Syntax

str.codePointAt(pos)

Parameters

pos

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

Return value

A number representing the code point value of the character at the given pos. If there is no element at pos, returns undefined.

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.

Polyfill

The following extends Strings to include the codePointAt() function as specified in ECMAScript 2015 for browsers without native support.

/*! https://mths.be/codepointat v0.2.0 by @mathias */
if (!String.prototype.codePointAt) {
  (function() {
    'use strict'; // needed to support `apply`/`call` with `undefined`/`null`
    var defineProperty = (function() {
      // IE 8 only supports `Object.defineProperty` on DOM elements
      try {
        var object = {};
        var $defineProperty = Object.defineProperty;
        var result = $defineProperty(object, object, object) && $defineProperty;
      } catch(error) {}
      return result;
    }());
    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
          // https://mathiasbynens.be/notes/javascript-encoding#surrogate-formulae
          return (first - 0xD800) * 0x400 + second - 0xDC00 + 0x10000;
        }
      }
      return first;
    };
    if (defineProperty) {
      defineProperty(String.prototype, 'codePointAt', {
        'value': codePointAt,
        'configurable': true,
        'writable': true
      });
    } else {
      String.prototype.codePointAt = codePointAt;
    }
  }());
}

Examples

Using codePointAt()

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

'XYZ'.codePointAt(42)          // undefined

Looping with codePointAt()

for (let codePoint of '\ud83d\udc0e\ud83d\udc71\u2764') {
   console.log(codePoint.codePointAt(0).toString(16))
}
// '1f40e', '1f471', '2764' 

Specifications

Browser compatibility

The compatibility table in this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.

See also

• String.fromCodePoint()
• String.fromCharCode()
• String.prototype.charCodeAt()
• String.prototype.charAt()