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";
Try it Yourself »
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"};
Try it Yourself »
The values are written as name:value pairs (name and value separated by a colon).
It is a common practice to declare objects with the const keyword.
Object Definition
You define (and create) a JavaScript object with an object literal:
Example
const person = {firstName:"John", lastName:"Doe", age:50, eyeColor:"blue"};
Try it Yourself »
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"
};
Try it Yourself »
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"]
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;
}
};
The this Keyword
In a function definition, this refers to the "owner" of the function.
In the example above, this is the person object that "owns" the
fullName function.
In other words, this.firstName means the firstName property of this object.
Read more about the this keyword at JS this Keyword.
Accessing Object Methods
You access an object method with the following syntax:
objectName.methodName()
If you access a method without the () parentheses, it will return the function definition:
Do Not Declare Strings, Numbers, and Booleans as Objects!
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
Avoid String, Number, and Boolean objects. They complicate your code and slow down
execution speed.
You will learn more about objects later in this tutorial.
