square brackets notation in riot.render about riot HOT 2 CLOSED

riot.render = function(tmpl, data, escape_fn) {
  if (escape_fn === true) escape_fn = default_escape_fn;
  tmpl = tmpl || '';

  return (FN[tmpl] = FN[tmpl] || new Function("_", "e", "return '" + 
    tmpl.replace(/[\\\n\r']/g, function(char) {
      return template_escape[char];
    }).replace(/{\s*(.+?)\s*}/g, function(m, g) {
        var key = g.split(".").reduce(function (acc, i) {
            return isNaN(i) ? acc + "['" + i + "']" : acc + "[" + i + "]";
        }, "");
        return "' + (e?e(_" + key + ",\"" + key + "\"):_" + key + "||(_" + key + "==null?'':_" + key + ")) + '";
    }) + "'")
  )(data, escape_fn);

};