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