Objects

Info:

• declare objects with the const keyword.

• JavaScript objects are written with curly braces {}

• Objects use named indexes.

  The values are written as name:value pairs (name and value separated by a colon).

  const car = {type:"Fiat", model:"500", color:"white"};

• Properties

  Object properties are written as name:value pairs, separated by commas.

  All cars have the same properties, but the property values differ from car to car.

• Methods

  All cars have the same methods, but the methods are performed at different times.

Declaration

Info:

• You define (and create) a JavaScript object with an object literal:

  const person = {firstName:"John", lastName:"Doe", age:50, eyeColor:"blue"};

• Spaces and line breaks are not important. An object definition can span multiple lines:

  const person = {
    firstName: "John",
    lastName: "Doe",
    age: 50,
    eyeColor: "blue"
  };

Danger:

• Do Not Declare Strings, Numbers, and Booleans as Objects!

  Avoid String, Number, and Boolean objects. They complicate your code and slow down execution speed.

  When a JavaScript variable is declared with the keyword "new", the variable is created as an object:

  x = new String();        // Declares x as a String object
  y = new Number();        // Declares y as a Number object
  z = new Boolean();       // Declares z as a Boolean object

Properties

Info:

• JavaScript objects are containers for named values called properties.

• The name:values pairs in JavaScript objects are called properties:

• You can access object properties in two ways:

  objectName.propertyName

  objectName["propertyName"]

Methods

Info:

• A method is a function stored as a property.

  Methods are actions that can be performed on objects.

  Methods are stored in properties as function definitions.

const person = {
  firstName: "John",
  lastName : "Doe",
  id       : 5566,
  fullName : function() {
    return this.firstName + " " + this.lastName;
  }
};

• Accessing Methods

  objectName.methodName()

  • If you access a method without the () parentheses, it will return the function definition:

    name = person.fullName;
    // returns: function() { return this.firstName + " " + this.lastName; }

this

• this keyword refers to an object

  I.E. this.firstName means the firstName property of this.

  I.E. this.firstName means the firstName property of person.

  const person = {
    firstName: "John",
    lastName : "Doe",
    id       : 5566,
    fullName : function() {
      return this.firstName + " " + this.lastName;
    }
  };

• The this keyword refers to different objects depending on how it is used

  • In an object method, this refers to the object.
  • Alone, this refers to the global object.
  • In a function, this refers to the global object.
  • In a function, in strict mode, this is undefined.
  • In an event, this refers to the element that received the event.
  • Methods like call(), apply(), and bind() can refer this to any object.