javascript

Chapter 22: The Evolution of JavaScript
The current ECMAScript 4 description provides no information about accessing superclass methods
from a subclass.
Final Classes and Methods
You can prevent classes from being extended and methods from being overridden by specifying either as
final . A final class can never be inherited from and any attempts to do this will result in an error;
likewise, final methods cannot be overridden in a subclass or an error will occur, as in this example:
class Person {
var name: string;
var age: int;
}
final function sayName(){
alert(this.name);
}
class Employee extends Person {
var job: string;
}
override function sayName(){
alert(this.name + “:” + this.job);
}
//error!!!
final class Friend extends Person {
}
In this example, the Person class method sayName() is specified as final so the Employee class cannot
override it. The Friend class is defined as final, so it can never be inherited from.
Namespaces
ECMAScript 4 introduces the concept of namespaces. Namespaces are compile - time values that group
functionality together. You can define a namespace by using the namespace directive as follows:
namespace myNamespace;
namespace xhtml = “http://www.w3.org/1999/xhtml/”;
Once a namespace is created, you can annotate classes, types, and the like as being part of the
namespace. Here’s an example:
myNamespace type Point = { x: int, y: int };
myNamespace class Box {
//more code here
}
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