un/escape HTML in Javascript

html-escape.js

// Use the browser's built-in functionality to quickly and safely escape the
// string
function escapeHtml(str) {
    var div = document.createElement('div');
    div.appendChild(document.createTextNode(str));
    return div.innerHTML;
};

// UNSAFE with unsafe strings; only use on previously-escaped ones!
function unescapeHtml(escapedStr) {
    var div = document.createElement('div');
    div.innerHTML = escapedStr;
    var child = div.childNodes[0];
    return child ? child.nodeValue : '';
};