Constructor function

Question

What is the difference between these two codes?

  let user = new function() {
      this.name = "John";
      this.isAdmin = false;
  }

vs

 let user =  {
    name: "John",
    isAdmin: false
}

Answer 1

The only difference is that the first user, created via new, has an internal prototype of a (nearly) empty object, and that empty object inherits from Object.prototype:

instance <- (empty object) <- Object.prototype

let user = new function() {
  this.name = "John";
  this.isAdmin = false;
};

console.log(user);

Technically, the object isn't entirely empty, it has a non-enumerable constructor property pointing to the function

This nearly empty object is the .prototype property of the function - but since that prototype object doesn't have any properties on it, it looks empty. If you had put properties on the function's .prototype object, these would be visible on the intermediate object:

function Foo() {
  this.name = "John";
  this.isAdmin = false;
}
Foo.prototype.prop = 'val';
let user = new Foo();

console.log(user);
console.log(Object.getPrototypeOf(user).hasOwnProperty('prop'));
console.log(Object.getPrototypeOf(user) === Foo.prototype);

The user from an object literal, on the other hand, inherits directly from Object.prototype:

instance <- Object.prototype

 let user =  {
    name: "John",
    isAdmin: false
}
console.log(Object.getPrototypeOf(user) === Object.prototype);

Answer 2

Firstly both of them create a new object and the following code inside them is assigned to the object. They then execute the code in the function body and can return the value.