I think the following code will make the question clear.

// My class

var Class = function() { console.log(Constructor); };

Class.prototype = { method: function() { console.log(Method);} }



// Creating an instance with new

var object1 = new Class();

object1.method();

console.log(New returned, object1);



// How to write a factory which can't use the new keyword?

function factory(clazz) {

    // Assume this function can't see Class, but only sees its parameter clazz.

    return clazz.call(); // Calls the constructor, but no new object is created

    return clazz.new();  // Doesn't work because there is new() method

};



var object2 = factory(Class);

object2.method();

console.log(Factory returned, object2);