function TemplateEngine(html, options) {
  var re = /<%([^%>]+)?%>/g, reExp = /(^( )?(if|for|else|switch|case|break|{|}))(.*)?/g, code = 'var r=[];\\n', cursor = 0, match;
  var add = function(line, js) {
    js ? (code += line.match(reExp) ? line + '\\n' : 'r.push(' + line + ');\\n')
       : (code += line != '' ? 'r.push("' + line.replace(/"/g, '\\\\"') + '");\\n' : '');
    return add;
  }
  while(match = re.exec(html)) {
    add(html.slice(cursor, match.index))(match[1], true);
    cursor = match.index + match[0].length;
  }
  add(html.substr(cursor, html.length - cursor));
  code += 'return r.join("");';
  return new Function(code.replace(/[\\r\\t\\n]/g, '')).apply(options);
}

Javascript-template-engine-in-just-20-line