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JavaScript Object

All things are JavaScript objects: strings, numbers, arrays, functions ...

In addition, JavaScript allows custom objects.

Everything is an object

JavaScript provides several built-in objects, such as String, Date, Array, and so on. Only with special data type object properties and methods.

  • Boolean can be an object.
  • Numeric type can be an object.
  • String can also be an object
  • Date is an object
  • Mathematics and regular expressions are objects
  • An array is an object
  • Even the object function may be

JavaScript Object

Object is just a special kind of data. Objects have properties and methods.

Property access objects

Property is a value associated with an object.

Access object attribute syntax is:


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

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

After the above code is executed, the value of x will be:


Object Access Method

The method is an operation that can be performed on the object.

You can call the method using the following syntax:


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

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

After the above code is executed, the value of x will be:


Create a JavaScript object

Through JavaScript, you can define and create your own objects.

Create a new object in two different ways:

  • Define and create an instance of an object
  • Use functions to define the object, and then create a new object instance

Create a direct instance

This example creates a new instance of the object and add four properties:


person=new Object();

try it"

Alternative syntax (using object literals):



try it"

Using the object constructor

This example uses the function to construct objects:


function person(firstname,lastname,age,eyecolor)

try it"

In JavaScript, this usually points to a function that we are executing itself, or an object that points to the function belongs to (run-time)

Create a JavaScript object instance

Once you have the object constructor, you can create a new instance of the object, like this:

var myFather=new person("John","Doe",50,"blue");
var myMother=new person("Sally","Rally",48,"green");

The properties to the JavaScript objects

You can assign an object, add new attributes to existing objects:

Suppose personObj already exists - which you can add these new attributes: firstname, lastname, age and eyecolor:



T in the above code is executed, the value of x will be:


The method to add objects to JavaScript

The method is simply attached to the object's function.

In the method of the constructor function inside the definition of an object:

function person(firstname,lastname,age,eyecolor)

	function changeName(name)

() Value of the function name of the person assigned to changeName lastname properties.

Now you can try:


try it"

JavaScript classes

JavaScript is an object-oriented language, but JavaScript does not use class.

In JavaScript, the class is not created, nor to create an object (as in the other object-oriented languages) through the class.

JavaScript-based prototype, rather than class-based.

JavaScript for ... in loop

JavaScript for ... in statement to loop through the object's properties.


for (variable in object)

Note: for ... in loop code block will be executed once for each property.


Loop through the properties of an object:


var person = {fname: "John", lname: "Doe", age: 25};

for (x in person)
txt = txt + person [x];

try it"