JavaScript Objects
A JavaScript object is a step up from a variable, which can contain only one value at a time, in that objects can contain multiple values and even functions. An object groups data together with the functions needed to manipulate it.
Declaring a Class
When creating a script to use objects, you need to design a composite of data and code called a class. Each new object based on this class is called an instance (or occurrence) of that class. As you’ve already seen, the data associated with an object are called its properties, while the functions it uses are called methods.
Let’s look at how to declare the class for an object called
User that will contain details
about the current user. To create the class, just write a function
named after the class. This function can accept arguments (I’ll show
later how it’s invoked) and can create properties and methods for the
objects in that class. The function is called a
constructor.
Example 16-5 shows
a constructor for the class User
with three properties: forename,
username, and password. The class also defines the method
showUser.
<script>
function User(forename, username, password)
{
this.forename = forename
this.username = username
this.password = password
this.showUser = function()
{
document.write("Forename: " + this.forename + "<br />")
document.write("Username: " + this.username + "<br />")
document.write("Password: " + this.password + "<br />")
}
}
</script>The function ...