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    String.prototype.codePointAt()

    This is an experimental technology, part of the ECMAScript 6 (Harmony) proposal.
    Because this technology's specification has not stabilized, check the compatibility table for usage in various browsers. Also note that the syntax and behavior of an experimental technology is subject to change in future version of browsers as the spec changes.

    Summary

    The codePointAt() method returns a non-negative integer that is the UTF-16 encoded code point value.

    Syntax

    str.codePointAt(pos)

    Parameters

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

    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

    Example: 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 6 (ECMA-262)
    The definition of 'String.prototype.codePointAt' in that specification.
    Release Candidate Initial definition.

    Browser compatibility

    Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
    Basic support 41 29 (29) 11 on Windows 10 Preview Not supported Not supported
    Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
    Basic support Not supported Not supported 29.0 (29) Not supported Not supported Not supported

    See also

    Document Tags and Contributors

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