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dotnet jscript : JavaScript class creation query
Dhruba Bandopadhyay <dhruba.bandopadhyay@hotmail.com> wrote: > I have came across 3 different ways of creating a structure or class. > > 1. Class as a function way > > // Class Constructor > function Timer(Source) { > > // Class Properties > this.timerID = 0; > this.tStart = null; > > // Class Methods > this.UpdateTimer = function() { > }; > } It's better to define a method like this: function Timer() {...} Timer.prototype.UpdateTimer = function() {...}; This way the function is created only once. In your original code, an instance of the function object is created anew every time an instance of Timer is created. [quoted text, click to view] > 2. Class.create & prototype way > > var WindowDelegate = Class.create(); I've never seen this syntax. In IE, it produces an error " 'Class' is undefined". [quoted text, click to view] > 3. Declare as a var way > > var myObserver = { > variable: null, > anotherVariable: 33 > stringVariable: 'asdf', > aFunction: function(a, b) { > } > } > > I assume #3 is just a object/structure instance rather than a class > definition. > > Has anyone came across #1 way? All major JavaScript libraries I know of do it this way. See e.g. http://dojotoolkit.org/ [quoted text, click to view] > What are the differences between these > 3 ways? Well, #2 does not work. #1 has a nice encapsulated syntax, constructors with parameters - you can almost pretend you are working in an object oriented language. #3 is useful for a quick one-off object, but this approach does not lend itself to reuse. Also, an object created with #1 can be tested with instanceof operator: var timer = new Timer(0); if (timer instanceof Timer) {...}; #3 also does not allow one to use prototype property to create a method just once: you have to define it every time you create an instance, which adds performance overhead. One can work around it like this, but it's not as clear as #1: function Timer_UpdateTimer() {...}; function makeTimer(source) { var timer = {}; // Class Properties timer.timerID = 0; timer.tStart = null; // Class Methods timer.UpdateTimer = Timer_UpdateTimer; } var timer = makeTimer(0); Almost everything you can do with #1 you can also do with #3, but I feel #1 syntax is cleaner. The two things you can only achieve with #1 are support for instanceof, and inheritance (in JavaScript, you can arrange for one class to "inherit" from another, several levels deep; multiple inheritance is not really supported, but there are techniques to fake it). [quoted text, click to view] > And what is the proper way to define a class? #1. -- With best wishes, Igor Tandetnik With sufficient thrust, pigs fly just fine. However, this is not necessarily a good idea. It is hard to be sure where they are going to land, and it could be dangerous sitting under them as they fly overhead. -- RFC 1925
I have came across 3 different ways of creating a structure or class.
1. Class as a function way // Class Constructor function Timer(Source) { // Class Properties this.timerID = 0; this.tStart = null; // Class Methods this.UpdateTimer = function() { }; } // Example var timer = new Timer(0); timer.UpdateTimer(); 2. Class.create & prototype way var WindowDelegate = Class.create(); WindowDelegate.prototype = { // Class Constructor initialize: function() { }, canClose: function(win) { } } 3. Declare as a var way var myObserver = { variable: null, anotherVariable: 33 stringVariable: 'asdf', aFunction: function(a, b) { } } I assume #3 is just a object/structure instance rather than a class definition. Has anyone came across #1 way? What are the differences between these 3 ways? And what is the proper way to define a class?
[quoted text, click to view] "Igor Tandetnik" <itandetnik@mvps.org> wrote in message news:uZpbV$DpGHA.4116@TK2MSFTNGP03.phx.gbl... > Dhruba Bandopadhyay <dhruba.bandopadhyay@hotmail.com> wrote: > > I have came across 3 different ways of creating a structure or class. > > > > 1. Class as a function way > > > > // Class Constructor > > function Timer(Source) { > > > > // Class Properties > > this.timerID = 0; > > this.tStart = null; > > > > // Class Methods > > this.UpdateTimer = function() { > > }; > > } > > It's better to define a method like this: > > function Timer() {...} > Timer.prototype.UpdateTimer = function() {...}; > > This way the function is created only once. In your original code, an > instance of the function object is created anew every time an instance > of Timer is created. > > > 2. Class.create & prototype way > > > > var WindowDelegate = Class.create(); > > I've never seen this syntax. In IE, it produces an error " 'Class' is > undefined". > > > 3. Declare as a var way > > > > var myObserver = { > > variable: null, > > anotherVariable: 33 > > stringVariable: 'asdf', > > aFunction: function(a, b) { > > } > > } > > > > I assume #3 is just a object/structure instance rather than a class > > definition. > > > > Has anyone came across #1 way? > > All major JavaScript libraries I know of do it this way. See e.g. > http://dojotoolkit.org/ > > > What are the differences between these > > 3 ways? > > Well, #2 does not work. #1 has a nice encapsulated syntax, constructors > with parameters - you can almost pretend you are working in an object > oriented language. #3 is useful for a quick one-off object, but this > approach does not lend itself to reuse. Also, an object created with #1 > can be tested with instanceof operator: > > var timer = new Timer(0); > if (timer instanceof Timer) {...}; > > #3 also does not allow one to use prototype property to create a method > just once: you have to define it every time you create an instance, > which adds performance overhead. One can work around it like this, but > it's not as clear as #1: > > function Timer_UpdateTimer() {...}; > function makeTimer(source) { > var timer = {}; > > // Class Properties > timer.timerID = 0; > timer.tStart = null; > > // Class Methods > timer.UpdateTimer = Timer_UpdateTimer; > } > var timer = makeTimer(0); > > > Almost everything you can do with #1 you can also do with #3, but I feel > #1 syntax is cleaner. The two things you can only achieve with #1 are > support for instanceof, and inheritance (in JavaScript, you can arrange > for one class to "inherit" from another, several levels deep; multiple > inheritance is not really supported, but there are techniques to fake > it). > > > And what is the proper way to define a class? > > #1. There are ultimately two 'proper' ways to define a class as you have already touched on. To clarify:- Option A. function MyClass(value) { var x = 0, y = 0 //private class level variables this.a = value // public member function fnPrivateStuff() // private functions { ... } this.publicStuff = function() // public method { ... } } This approach provides much stronger encapsulation (x,y for example can only be referenced from a function defined inside the class) it is therefore more suited to large complex objects. However as pointed out instances of this type are more expensive to create so may not be the best choice if a large number are to be created. A more important point IMO is that implementing a design that incoporates generalised and specialised classes (inheritance) is awkward in this approach. Option B function MyClass(value) { this.x = 0; this.y = 0 this.a = value } MyClass.prototype.fnPrivateStuff = function() { } MyClass.prototype.publicStuff = function() { } MyClass.prototype.publicStuff2 = function() { } This approach has much weaker encapsulation. In fact it has no encapsulation at all. The distinction between public and private members would have to rely on conventions such as the use of a preceeding underscore in member names. Creating a large number of instances of this class is cheaper since the created instance only needs to carry the value the member variables not the functions. This approach's biggest strength is in implementing specialisation of general classes:- function MyDerivedClass(value1, value2) { MyClass.call(this, value1) //Base class constructor this.b = value2 } MyDerivedClass.prototype = new MyClass() MyDerivedClass.prototype.somePublicMethod = function() { } MyDerivedClass.prototype.publicStuff2 = function() // override { } On thing often missed in the prototype approach is that default values for non-function members can also be defined. This further reduces the cost of creating instances of these classes where member values are only actually created when a new value is assigned to them. The MyClass above can look like this:- function MyClass(value) { this.a = value } MyClass.prototype.x = 0 MyClass.prototype.y = 0 HTH, Anthony
[quoted text, click to view]
"Dhruba Bandopadhyay" <dhruba.bandopadhyay@hotmail.com> wrote in message news:%23oIqfpDpGHA.1592@TK2MSFTNGP04.phx.gbl... > Has anyone came across #1 way? What are the differences between these 3 > ways? I recently made two fairly detailed posts about this on my blog: http://blogs.msdn.com/ptorr/archive/2006/06/13/630208.aspx http://blogs.msdn.com/ptorr/archive/2006/06/19/638195.aspx A third is on the way... [quoted text, click to view] > And what is the proper way to define a class? Tecnically these are not classes and there is no "right" or "wrong" way of doing it -- if the interpreter doesn't blow up, clearly you've done something right :-) Peter -- Peter Torr - http://blogs.msdn.com/ptorr HD DVD Program Manager
Net neutrality
class free society school is over (that one was deleted by ms) We don't want to be "classified" as lusers, users or idiots. -------------------------------------------- The net as is, is a keeper. We paid for it for 10 years plus. We own it. We shall cause uncomfort to anyone, tresspassing our ways and means and believes of the Internet as is. Never without our consent. We don't want an iraque modell of conquest to hush potentil progress other than fuzzy Texan business laws.. -------------- Let the old guys the US Congress know that ! ========================= I am not a Bush fan, but I know when he rides a bike, he is clear in his mind. He just does not understand to communicate beyond his education. .. [quoted text, click to view] "Peter Torr (MS)" <ptorr@microsoft.com> wrote in message
news:OqCizNcpGHA.4848@TK2MSFTNGP03.phx.gbl... > "Dhruba Bandopadhyay" <dhruba.bandopadhyay@hotmail.com> wrote in message > news:%23oIqfpDpGHA.1592@TK2MSFTNGP04.phx.gbl... > > > Has anyone came across #1 way? What are the differences between these 3 > > ways? > > I recently made two fairly detailed posts about this on my blog: > > http://blogs.msdn.com/ptorr/archive/2006/06/13/630208.aspx > > http://blogs.msdn.com/ptorr/archive/2006/06/19/638195.aspx > > A third is on the way... > > > And what is the proper way to define a class? > > Tecnically these are not classes and there is no "right" or "wrong" way of > doing it -- if the interpreter doesn't blow up, clearly you've done > something right :-) > > Peter > > -- > Peter Torr - http://blogs.msdn.com/ptorr > HD DVD Program Manager > >
correction
" than fuzzy Texan business laws.." should be "hurting fuzzy Texan business laws.." [quoted text, click to view] "asdf" <asdf@asdf.com> wrote in message
news:OQafkQxqGHA.4408@TK2MSFTNGP04.phx.gbl... > Net neutrality > class free society > school is over (that one was deleted by ms) > > We don't want to be "classified" as lusers, users or idiots. > -------------------------------------------- > The net as is, is a keeper. > > We paid for it for 10 years plus. > > We own it. > > We shall cause uncomfort to anyone, > tresspassing our ways and means and believes > of the Internet as is. > > Never without our consent. > > We don't want an iraque modell of conquest > to hush potentil progress other than fuzzy Texan business laws.. > -------------- > Let the old guys the US Congress know that ! > > ========================= > > I am not a Bush fan, but I know when he rides a bike, > he is clear in his mind. > > He just does not understand to communicate beyond his > education. > > > > . > > > > > "Peter Torr (MS)" <ptorr@microsoft.com> wrote in message > news:OqCizNcpGHA.4848@TK2MSFTNGP03.phx.gbl... > > "Dhruba Bandopadhyay" <dhruba.bandopadhyay@hotmail.com> wrote in message > > news:%23oIqfpDpGHA.1592@TK2MSFTNGP04.phx.gbl... > > > > > Has anyone came across #1 way? What are the differences between these 3 > > > ways? > > > > I recently made two fairly detailed posts about this on my blog: > > > > http://blogs.msdn.com/ptorr/archive/2006/06/13/630208.aspx > > > > http://blogs.msdn.com/ptorr/archive/2006/06/19/638195.aspx > > > > A third is on the way... > > > > > And what is the proper way to define a class? > > > > Tecnically these are not classes and there is no "right" or "wrong" way of > > doing it -- if the interpreter doesn't blow up, clearly you've done > > something right :-) > > > > Peter > > > > -- > > Peter Torr - http://blogs.msdn.com/ptorr > > HD DVD Program Manager > > > > >
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