template.js

var template = function (str, options) {
  var re = /{{(.+?)}}/g,
      reExp = /(^( )?(var|if|for|else|switch|case|break|{|}|;))(.*)?/g,
      code = 'with(obj) { var r=[];\n',
      cursor = 0,
      result,
      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(str)) {
    add(str.slice(cursor, match.index))(match[1], true);
    cursor = match.index + match[0].length;
  }

  add(str.substr(cursor, str.length - cursor));
  code = (code + 'return r.join(""); }').replace(/[\r\t\n]/g, '');

  try {
    result = new Function('obj', code).apply(options, [options]);
  }
  catch (err) {
    console.error("'" + err.message + "'", " in \n\nCode:\n", code, "\n");
  }

  return result;
};

template('<span id="{{key}}">{{value}}</span>', {key:'monkey_id',value:'monkey'});
//"<span id="monkey_id">monkey</span>"