In Ruby, I can add and modify functionality of any class, object, or method using the same syntax I would to declare my own because Ruby has "open classes".
Is javascript like that?
.
As an example...
In my case, I want to change the way Google Apps Script handles URL objects so that every time I evaluate a URL object, the URL object itself makes sure it begins with a protocol :// (http:// by default).
Yes, you can modify objects freely. You can modify a particular object Object.overridenProperty = ..., or modify all objects derived from a given class via its prototype property Object.prototype.inheritedMethod = ....
Have in mind that redefining a method can be tricky, as the new definition won't share the same scope as the original definition:
var BaseClass;
(function(){
var defaults = { ... };
BaseClass = function(){
this.someValue = defaults.someValue;
};
}());
It could also happen that the class definition lies inside a closure and you have no practical way to override a method or property as it is generated JIT. In that case you'd need to override the property at each object you are interested in individually:
(function(){
var defaults = { ... },
BaseObject = (function(){
var obj = function(){
this.someValue = defaults.someValue;
};
return obj;
}());
}());
Yes.
With the caveat that how you define a "class" is pretty different than in Ruby. But you can achieve the same effect.
This ruby:
#ruby
class Foo
# no methods yet
end
foo = Foo.new
class Foo
def bar
'bar'
end
end
foo.bar #=> 'bar'
Would have this equivalent JavaScript implementation:
// js
var Foo = function() {};
var foo = new Foo();
Foo.prototype.bar = function() {
return 'bar';
};
foo.bar(); // 'bar'
You can even override things just as easily:
var oldBar = Foo.prototype.bar;
Foo.prototype.bar = function() {
return "Called oldBar and got: "+ oldBar.call(this);
};
foo.bar(); // "Called oldBar and got: bar"
see this class with getter and setter:
function User(){
this._name = "";
}
User.prototype.setName = function(name){this._name = name;}
User.prototype.getName = function(){return this._name;}
user = new User();
user.setName("somename");
alert(user.getName(););
You've specifically mentioned Google Apps Script in your question. Since GAS is a variant of JavaScript, the "usual methods" of object definition and extension apply, as covered in the other answers.
However, there's one terribly annoying exception: You cannot extend prototypes of Google's Classes. You can find comments about this on the issue tracker, Issue 708. It's been marked "Won't Fix".
