Context of nested functions inside object literal? [duplicate]

This question already has an answer here:

• How does the “this” keyword work? 20 answers

var obj ={ function1: function(){
    console.log('function1', this);
    return function function2(){
        console.log('function2', this);
        return function function3(){
             console.log('function3', this);
        };
    };
  };};

 var f1 = new function1();//function1 function1 {}
 var f2 = new f1();//function2 function2 {}
 var f3 = f2();//function3 Window {postMessage: ƒ, blur: ƒ, focus: ƒ, close: ƒ, frames: Window, …}
     f3 = new f2();//function3 function3 {}

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Why is it that in function3 'this' is bound to 'Window' object when invoked without 'new' prefix. Shouldn't 'this' be bound to the object 'obj' which owns it?