What is the reason to use the 'new' keyword at Derived.prototype = new Base

Question

What does the following code do:

WeatherWidget.prototype = new Widget;

where Widget is a constructor, and I want to extend the

Answer 1

new is important for prototype inheritance; i.e.
Create a constructor with a method

var Obj = function(){};
Obj.prototype = {};
Obj.prototype.foo = function(){console.log('foo');};

Make a second constructor to extend the first with

var ExObj = function(){};

Now, if we prototype without new,

ExObj.prototype = Obj;
(new ExObj).foo(); // TypeError: Object #