07-object-oriented-programming.md

How do I add a method to an object?

let duck = {
  sayName: function() {
    return "The name of this duck is " + duck.name + ".";
  }
};

How do I refer to the object within one of its method?

Use this:

let duck = {
  sayName: function() {return "The name of this duck is " + this.name + ".";}
};

How do I define a constructor?

function Bird() {
  this.name = "Albert";
  this.color = "blue";
  this.numLegs = 2;
}

What conventions should I follow when creating a constructor?

1. Capitalized name
2. Use this to set properties on the new object it will create.
3. Doesn't return anything

Question: Can constructors use ES6 syntax?

How do you call a constructor?

let blueBird = new Bird();

How do I verify if an object was created by a constructor?

crow instanceof Bird; // => true

What are "own properties"?

Properties defined directly on the instance object.

How do I iterate over the properties of an object?

for (let property in duck) {
}

How do I check if a property is an object's own property?

  if(duck.hasOwnProperty(property)) {
  }

How do I share a property across all instances of a class?

Bird.prototype.numLegs = 2;

Where does the prototype belong?

Part of the constructor

What are the kinds of properties?

• Own properties
• Prototype properties

How do I get the constructor of an object?

object.constructor

How is .constructor different from instanceof?

How do I set multiple properties for a prototype?

Bird.prototype = {
  numLegs: 2,
  eat: function() {
    console.log("nom nom nom");
  },
  describe: function() {
    console.log("My name is " + this.name);
  }
};

What happens to the constructor when an object is assigned to a property?

It gets erased?

Does instanceof still work though?

Yes:

duck.constructor === Bird; // false -- Oops
duck instanceof Bird; // true, still works

How do we fix this?

Manually set the constructor when setting the prototype to an object:

Bird.prototype = {
  constructor: Bird,

  // ...
}

What is the relationship of a new object's prototype with its constructor's prototype?

The new object's prototype is inherited from the constructor's prototype:

Bird.prototype.isPrototypeOf(duck);

What is the type of prototypes?

typeof Bird.prototype; // yields 'object'

Do prototypes have prototypes?

Yes, because a prototype is of object type, and (almost) all objects have prototypes.

How do I create an object in a manner that respects inheritance?

let animal = Object.create(Animal.prototype);

How do I properly let a subclass inherit from a superclass?

Bird.prototype = Object.create(Animal.prototype);
Bird.prototype.constructor = Bird;

How do you define a mixin in JS?

let flyMixin = function(obj) {
  obj.fly = function() {
    console.log("Flying, wooosh!");
  }
};

How do I create a private variable?

Inside the constructor function:

function Bird() {
  let hatchedEgg = 10; // private variable
}

What is closure?

When a function has access to the context in which it was created

How do I grant a method access to a private variable?

function Bird() {
  let hatchedEgg = 10; // private variable

  /* publicly available method that a bird object can use */
  this.getHatchedEggCount = function() {
    return hatchedEgg;
  };
}

What do we call (function() {})()?

Immediately invoked function expression

Where are IIFEs used?

With modules.