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JavaScript Objects HTML DOM ObjectsJavaScript Objects
"Everything" in JavaScript is an Object: a String, a Number, an Array, a Date....
In JavaScript, an object is data, with properties and methods.
Properties and Methods
Properties are values associated with an object.
Methods are actions that can be performed on objects.
A Real Life Object. A Car:
Properties:car.name=Fiatcar.model=500 car.weight=850kg car.color=white |
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Methods:car.start()car.drive() car.brake() |
The properties of the car include name, model, weight, color, etc.
All cars have these properties, but the values of those properties 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.
When you declare a JavaScript variable like this:
var txt = "Hello";
You actually create a JavaScript String object. The String object has a built-in property called length. For the string above, length has the value 5. The String object also have several built-in methods.
Properties:txt.length=5 |
"Hello" |
Methods:txt.indexOf()txt.replace() txt.search() |
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In object oriented languages, properties and methods are often called object members. |
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You will learn more about properties and the methods of the String object in a later chapter of this tutorial.
Creating JavaScript Objects
Almost "everything" in JavaScript is an object. 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
person=new Object();
person.firstname="John";
person.lastname="Doe";
person.age=50;
person.eyecolor="blue";
person.firstname="John";
person.lastname="Doe";
person.age=50;
person.eyecolor="blue";
Try it yourself »
There are many different ways to create new JavaScript objects, and you can also add properties and methods to existing objects.
You will learn much more about this in a later chapter of 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;
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();
var x=message.toUpperCase();
The value of x, after execution of the code above will be:
HELLO WORLD!
Did You Know?
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It is common in object oriented languages, to use camel-case function names. You will more often see function names like someMethod() instead of some_method(). |
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