1. Use constructor functions to make creating multiple similar objects easy
1. Create a base class which can be used to create child classes
1. Use prototype to assign properties to a class
1. Assign the correct prototype to a sub class
1. Correctly assign the constructor of a child class
## Use JavaScript objects to model the real world
@ -149,3 +152,122 @@ var Humvee = function(){
var murica = new Humvee();
console.log(murica);
```
## Use prototype to assign properties to a class
The problem with using `this.wheels = 4` inside a constructor function is that the code runs each time you create a new object. This is redundant.
Instead we can assign the property to the function's `.prototype` property instead.
```javascript
var Car = function(){
}
Car.prototype.wheels = 4;
var myCar = new Car();
console.log(myCar.wheels);
```
- `Car.prototype.wheels = 4;` runs only once, but all instances of the Car class have the wheels property already set. You can do this with any property you want
- If you do `console.log(myCar)` you'll notice that you can inspect the prototype of the Class of the object by looking at the `.__proto__` property. There you'll find the .wheels property you added to `Car.prototype`
- When you look for a property of an object, it will first look on the object itself, then on its prototype, then on the prototype's prototype, etc...
## Assign the correct prototype to a sub class
If we are using prototype to add methods and properties to our class, our inheritance process gets a little tricky
```javascript
var Person = function(){
}
Person.prototype.legs = 2;
Person.prototype.arms = 2;
var Student = function(){
Person.call(this);
}
var matt = new Student();
console.log(matt.legs); //returns undefined?!
```
To fix this, we need to assign a person object to the `Student.prototype` property
```javascript
var Person = function(){
}
Person.prototype.legs = 2;
Person.prototype.arms = 2;
var Student = function(){
Person.call(this);
}
Student.prototype = Object.create(Person.prototype); //create a Person object, then assign it to the Student.prototype
var matt = new Student();
console.log(matt.legs); //returns 2
```
Now we've created a Person object and assigned it to the to Student's prototype property. Now when a Student object looks for `.legs` it will go to the Student's `__proto__` (Person object) and then the `__proto__` of that object.
## Correctly assign the constructor of a child class
A good way to check a constructor is to log the `.__proto__.constructor` property:
GitHub