TOP - Objects and Object Constructors

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Introduction

There are multiple ways to define objects but in most cases, it is best to use the object literal syntax as follows:

const myObject = {
  property: 'Value!',
  otherProperty: 77,
  "obnoxious property": function() {
    // do stuff!
  }
};

There are also 2 ways to get information out of an object:

1. dot notation myObject.property; // 'Value!'
2. square bracket notation myObject["obnoxious property"]; // [Function]

Which method you use will depend on context. Dot notation is cleaner and is usually preferred

you cannot use variables in dot notation:

const variable = 'property';

myObject.variable; // this gives us 'undefined' because it's looking for a property named 'variable' in our object

myObject[variable]; // this is equivalent to myObject['property'] and

Lesson overview

This section contains a general overview of topics that you will learn in this lesson.

• How to write an object constructor and instantiate the object.
• Describe what a prototype is and how it can be used.
• Explain prototypal inheritance.
• Understand the basic do’s and don’t’s of prototypal inheritance.
• Explain what Object.create does.
• Explain what the this keyword is.

Object constructors

When you have a specific type of object that you need to duplicate like our player or inventory items, a better way to create them is using an object constructor, which is a function that looks like this:

function Player(name, marker) {
  this.name = name;
  this.marker = marker;
}

and which you use by calling the function with the keyword new.

const player = new Player('steve', 'X');
console.log(player.name); // 'steve'

Just like with objects created using the Object Literal method, you can add functions to the object:

function Player(name, marker) {
  this.name = name;
  this.marker = marker;
  this.sayName = function() {
    console.log(name)
  };
}

const player1 = new Player('steve', 'X');
const player2 = new Player('also steve', 'O');
player1.sayName(); // logs 'steve'
player2.sayName(); // logs 'also steve'

Exercise

• Write a constructor for making “Book” objects
• Your book objects should have the book's title, author and number of pages, and whether or not you have read the book
• Put a function into the constructor that can report the book info like so:

theHobbit.info(); // "The Hobbit by J.R.R. Tolkien, 295 pages, not read yet"

The prototype