Spot the bugs

Animal.js

const Animal = (name, type) => {
  this.name = name
  this.type = type
  this.age = 0
}

Animal.prototype.birthday = function () {
  this.age++
}

const leo = new Animal('Leo', 'Lion')

/*
Arrow Functions don't have their own `this`. This leads to three errors in our code.

First, we're adding properties to `this` in the constructor function. Again, because
Arrow Functions don't have their own `this`, you can't do that.

Second, we can't use the `new` keyword with an Arrow Function. This will throw a `X is
not a constructor` error.

Third, we can't add a property on a function's prototype if that function is an Arrow
Function, again, because there's no `this`.
*/

// Solution

function Animal (name, type) {
  this.name = name
  this.type = type
  this.age = 0
}

Animal.prototype.birthday = function () {
  this.age++
}

const leo = new Animal('Leo', 'Lion')