couple of tricks about prototypal inheritance

proto-tricks.js

/**
 * understanding .constructor property
 */

function User() {

}

// when functions are created, they're given a "prototype" property which is an object
console.log(User.prototype);  // {}
// tne only property of that prototype object is "constructor" which points back to the function that was created with
console.log(User.prototype.constructor); // User

const jero = new User();

console.log(jero.constructor === User) // true;


/**
 * Looping over properties
 */

const user = {
  name: 'Jero',
  url: 'https://someurl.com'
};

let i = 0;

for (property in user) {
  i += 1;
}

i // 2

// Loops can behave differently when objects have chained prototype objects.

const user = {
  name: 'Jero',
  url: 'https://someurl.com'
};

const protoUser = {
  email: 'some@email.com'
};

Object.setPrototypeOf(user, protoUser);

let i = 0;

for (property in user) {
  i += 1;
}

i // 3, and that's because for-in loop steps through the prototype chain object-by-object

// to avoid that just simply iterate over object's own properties
for (property in user) {
  if(obj.hasOwnProperty(property)){
    i += 1;
  }
}

i // 2