Constructor functions hold an interesting purpose in JavaScript. Unlike in classical languages, they do not always mean created by. In this lesson we’ll use the new keyword to make a constructor call and work with the .constructor property.

When we define a function:

function Foo(){
    
 
//.
}

It has one prototype prop defined which is constructor. And it points to the Foo function itself.

console.log(Foo.prototype.constructor === Foo) // true

And if we have an instance created by new keyword:

const f= new Foo();

Then:

console.log(f.constructor === Foo) // true
 

So which mean:

f.constructor === Foo.prototype.constructor

This prototype chain can be broken when we reassgin the Foo.prototype = {}:

Foo.prototype = {}; // now we reassign to an empty object.
console.log(Foo.prototype.constructor === Foo);  // false
console.log(f.constructor === Foo); //
 
true
console.log(f.constructor === Foo.prototype.constructor); // false

We can use Object.defineProperty to reassign the constructor to the Foo.prototype:

Foo.prototype = {};
Object.defineProperty(Foo.prototype, "constructor", {
  enumerable: false,
  writable: true,
  configurable: true,
  value: Foo
});

console.log(Foo.prototype.constructor === Foo); // true
console.log(f.constructor === Foo); // true
console.log(f.constructor === Foo.prototype.constructor); // true