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JavaScript Objects


Almost everything in JavaScript can be an Object: Strings, Functions, Arrays, Dates....

Objects are just data, with added properties and methods.


Properties and Methods

Properties are values associated with objects.

Methods are actions objects can perform.


A Real Life Object. A Car:

Object Properties Methods

car.name = Fiat

car.model = 500

car.weight = 850kg

car.color = white

car.start()

car.drive()

car.brake()

The properties of the car include name, model, weight, color, etc.

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

The methods of the car could be start(), drive(), brake(), etc.

All cars have these methods, but they are performed at different times.


Objects in JavaScript:

In JavaScript, objects are data (variables), with properties and methods.

You create a JavaScript String object when you declare a string variable like this:

var txt = new String("Hello World");

 String objects have built-in properties and methods:

Object Property Method
"Hello World" txt.length
txt.indexOf("World")

The string object above has a length property of 11.

The indexOf("World") method will return 6 (0 is position 1).

Note

In object oriented languages, properties and methods are often called object members.

You will learn more about properties and methods of the String object later in this tutorial.


Creating JavaScript Objects

Almost "everything" in JavaScript can be objects. Strings, Dates, Arrays, Functions....

You can also create your own objects.

This example creates an object called "person", and adds four properties to it:

Example

var person {firstname:"John", lastname:"Doe", age:50, eyecolor:"blue"};

Try it yourself »

There are many different ways to create new JavaScript objects, and you can also add new properties and methods to already existing objects.

You will learn much more about objects later in this tutorial.


Accessing Object Properties

The syntax for accessing the property of an object is:

objectName.propertyName

This example uses the length property of the String object to find the length of a string:

var message = "Hello World!";
var x = message.length;

The value of x, after execution of the code above will be:

12


Accessing Object Methods

You can call a method with the following syntax:

objectName.methodName()

This example uses the toUpperCase() method of the String object, to convert a text to uppercase:

var message = "Hello world!";
var x = message.toUpperCase();

The value of x, after execution of the code above will be:

HELLO WORLD!


Did You Know?


Note
It is common, in object oriented languages, to use camel-case names.
You will often see names like someMethod(), instead of some_method().



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