Learn JS #10

Posted on by Apostube

JavaScript Objects

Real Life Objects, Properties, and Methods

In real life, a car is an object.

A car has properties like weight and color, and methods like start and stop:

Object Properties Methods
car.name = Fiat

car.model = 500

car.weight = 850kg

car.color = white

 car.start()

car.drive()

car.brake()

car.stop()

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

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

JavaScript Objects

You have already learned that JavaScript variables are containers for data values.

This code assigns a simple value (Fiat) to a variable named car:

let car = "Fiat";

Objects are variables too. But objects can contain many values.

This code assigns many values (Fiat, 500, white) to a variable named car:

const car = {type:"Fiat", model:"500", color:"white"};
The values are written as name:value pairs (name and value separated by a colon).

Object Definition

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

Example

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

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

Example

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

Object Properties

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

Property Property Value
firstName John
lastName Doe
age 50
eyeColor blue

Accessing Object Properties

You can access object properties in two ways:

objectName.propertyName

or

objectName["propertyName"]

Example1

person.lastName;

Example2

person["lastName"];

JavaScript objects are containers for named values called properties.

Object Methods

Objects can also have methods.

Methods are actions that can be performed on objects.

Methods are stored in properties as function definitions.

Property Property Value
firstName John
lastName Doe
age 50
eyeColor blue
fullName function() {return this.firstName + ” ” + this.lastName;}

A method is a function stored as a property.

Example

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

In the example above, this refers to the person object.

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

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

Apostube

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