What is instance.constructor.constructor and how does it work?

Question

function Person(name) {
    this.name = name;
}   

let person1 = new Person("Eve");

person1.constructor; // Output: ƒ Person(name) {}

person1.constructor.constructor; // Output: ƒ Function() { [native code] }

person1.constructor.constructor("console.log(1)"); // Output: ƒ anonymous() {console.log(1)}

person1.constructor.constructor("console.log(1)")(); // Output: 1

Can someone help me to understand person1.constructor.constructor , person1.constructor.constructor("console.log(1)") and person1.constructor.constructor("console.log(1)")() ? I do not understand the outputs.

Answer 1

The .constructor property of an instance points to the function associated with the internal prototype. As you can see, person1.constructor gives you Person , because person1 was created with new Person ( person1 's internal prototype is Person.prototype )

What is the Person ? It's a function. The .constructor of a function will be the function associated with the internal prototype of that function - that is, the constructor associated with Function.prototype , which is Function , the function constructor:

 function Person(name) { this.name = name; } let person1 = new Person("Eve"); console.log(person1.constructor.constructor === Function);

You can pass strings to new Function to create functions out of them.

person1.constructor.constructor("console.log(1)");

is just like

Function("console.log(1)");

which returns a function that, when called, logs 1.

 const fn = Function("console.log(1)"); console.log(fn); fn();