/**
 * replace all :emoji: codes with corresponding image
 * @param {string} inputString
 * @return {string}
**/
function formatEmojis(inputString) {
    return inputString.replace(/:([^ \t:]+):/g, function(returnFailed, emoji) {
        var emojiDom = makeEmojiDom(emoji);
        if (emojiDom) {
            var domParent = document.createElement("span");
            domParent.className = returnFailed === inputString ? R.klass.emoji.medium : R.klass.emoji.small;
            domParent.appendChild(emojiDom);
            return domParent.outerHTML;
        }
        return returnFailed;
    });
}