Difference between constructor function and instance

A constructor function is the function we use to create a custom object in JavaScript, while an instance is a just that - an instance of our custom Object. Take a custom object, Animal:

// constructor function
func Animal(name, soundItMakes) {
  this.name = name
  this.soundItMakes = soundItMakes
}
// an instance
var cow = new Animal("cow", "moo") // returns Animal { name: "cow", soundItMakes: "moo" }
// another instance
var sheep = new Animal("sheep", "baa") // returns Animal { name: "sheep", soundItMakes: "baa" }

So anytime you see the keyword "new", that's a clue that you're looking at an instance. If you're seeing a function, chances are that it's a constructor function. Hope this helps.

The first thing you should know is that a constructor is dependent on having an instance. So you first need to know what an instance is. An instance is just a representation of an object. So like how a cow or a dog is a representation of an animal.

So what the constructor does is run code at the moment you create the instance. So if you want to create a dog and at the time of creation you want to give it a name like Scruffy that would be the constructor code. By constructor code I mean the code to set name = scruffy.