JavaScript objects
JavaScript Objects
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 | Car.name=Fiat | Car.Start() | |
| Car.model=500 | Car.drive() | ||
| Car.weight=850kg | Car.broke() | ||
| Car.color=white | 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.
You have already learned that JavaScript variables are
containers for data values.
This code assigns a simple
value (Fiat) to a variable named car:
var car="Fiat";
<!DOCTYPE
html>
<html>
<body>
<p>Creating
a JavaScript Variable.</p>
<p
id="demo"></p>
<script>
var
car = "Fiat";
document.getElementById("demo").innerHTML
= car;
</script>
</body>
</html>
Objects
are variables too. But objects can contain many values.
This
code assigns many values (Fiat, 500, white) to a variable named car:
var car = {type:"Fiat",
model:"500", color:"white"};
<!DOCTYPE
html>
<html>
<body>
<p>Creating
a JavaScript Object.</p>
<p
id="demo"></p>
<script>
var
car = {type:"Fiat", model:"500", color:"white"};
document.getElementById("demo").innerHTML
= car.type;
</script>
</body>
</html>
The
values are written as name:value pairs (name and value separated by a colon).
Note JavaScript objects are containers for named
values.
Object Properties
The name:values pairs (in JavaScript objects) are called
properties.
var person = {firstName:"John",
lastName:"Doe", age:50, eyeColor:"blue"};
| Property | PropertyValue |
|---|---|
| FirstName | John |
| LastName | Doe |
| Age | 50 |
| eyecolor | blue |
Object Methods
Methods
are actions that can be performed on objects.
Methods
are stored in properties as function definitions.
| Property | PropertyValue |
|---|---|
| FirstName | John |
| LastName | Doe |
| Age | 50 |
| eyecolor | blue |
| fullName | function() { return this.firstName+" " +this.lastName;} |
JavaScript objects are containers for named values (called
properties) and methods.
Object Definition
You define (and create) a JavaScript object with an
object literal:
Example
var person = {firstName:"John",
lastName:"Doe", age:50, eyeColor:"blue"};
Spaces and line breaks are not important. An object
definition can span multiple lines:
Example
var person = {
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"];
Accessing Object Methods:
You access an object method with the following
syntax:
objectName.methodName()
Example
name = person.fullName();
If you access the fullName property, without (), it
will return the function definition:
Example
name = person.fullName;
<!DOCTYPE
html>
<html>
<body>
<p>An
object method is a function definition, stored as a property value.</p>
<p>If
you access it without (), it will return the function definition:</p>
<p
id="demo"></p>
<script>
var
person = {
firstName: "John",
lastName : "Doe",
id
: 5566,
fullName : function() {
return this.firstName + " " +
this.lastName;
}
};
document.getElementById("demo").innerHTML
= person.fullName;
</script>
</body>
</html>
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:
var
x = new String(); // Declares x as
a String object
var
y = new Number(); // Declares y as
a Number object
var
z = new Boolean(); // Declares z as a Boolean object
Avoid String, Number, and Boolean objects. They
complicate your code and slow down execution speed.
Objects
Adding Methods to Our Own Objects
Objects
Creating Our Own Objects
Object Initializers
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