code: function(target /*, obj...*/) {
      var args = Array.prototype.slice.call(arguments, 0),
          current, key, val;
  
      args.shift();
      current = args.shift();
      while(current) {
        for (key in current) {
          if (typeof target[key] === "undefined") {
            target[key] = current[key];
          }
        }
        current = args.shift();
      }
      return target;
    }
docs: For each `key`, `val` in each of `obj...`, set `target[key]` = `val` if `target[key]` is undefined