Unicode GroupMe Emoji Replacement

gistfile1.js

function codePointAt(text, position) {
	if (text == null) {
		throw TypeError();
	}
	var string = String(text);
	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;
};

function replaceEmojiUnicode(text) {
	text = text.replace(/([\u2002-\u3299])/g, function(match) {
		var code = match.charCodeAt(0);
		var codeHex = code.toString(16).toLowerCase();
		while (codeHex.length < 4) {
			codeHex = "0" + codeHex;
		}
		return '<img src="https://d2xk3mdboeujlo.cloudfront.net/images/emoji/64/' + codeHex + '.png" class="emoji">';
	});
	text = text.replace(/([\ud800-\udbff][\udc00-\udfff])/g, function(match) {
		var code = codePointAt(match, 0);
		var codeHex = code.toString(16).toLowerCase();
		while (codeHex.length < 4) {
			codeHex = "0" + codeHex;
		}
		return '<img src="https://d2xk3mdboeujlo.cloudfront.net/images/emoji/64/' + codeHex + '.png" class="emoji">';
	});
	return text;
}