extend. the one and only

extend.js

function extend () {
  return [].reduce.call(arguments, function (prev, current) {
    for (var prop in current) {
      if (!current.hasOwnProperty(prop)) continue;
      if (/^(object|array)$/.test(type(current[prop])) && current[prop] !== current) {
        if (!/^(object|array)$/.test(type(prev[prop]))) {
          prev[prop] = type(current[prop]) === 'array' ? [] : {};
        }
        prev[prop] = extend(prev[prop], current[prop]);
      } else {
        prev[prop] = current[prop];
      }
    }
    return prev;
  }, {});
}


function type(o) {return Object.prototype.toString.call(o).match(/\[object (.*?)\]/)[1].toLowerCase();}

To be used with type.js