String.prototype.codePointAt()

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

Browser compatibility

See also

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