All posts by abhishek.tiwari

Inheritance in JavaScript

May 17, 2010 21:26 by abhishek.tiwari

You may know it before that we can implement OOPs concepts in Javascript. I am going to demonstrate here one of them "Inheritance in Javascript".
Before going head let me tell you some facts about javascript

In javascript every function can be used to create an object out of it with "new" operator.
Javascript objects are hashed and interpreted that means you can add any property to them on runtime.
Every function (when used as class) is inherited by an inbuilt function(class) called "prototype" of that function. the constructor of your function/class is implemented inside the prototype of your function/class. So whatever properties or methods you add in prototype would be available to all objects of your function/class by default.
When any property/method is accessed from an object, interpreter first tries to find it inside the object itself, if it is not there then it looks into prototype class of that object and keeps on going up in its prototype chain unless it finds it. the super base of any object is prototype of "object" class itself. If it does not find it after crawling upto "object" prototype then it throws error of "undefined" or "not found".

Now let me give you an example how to implement inheritance

function Person()

{

this.eyes = 2;

this.legs = 2;

this.color = "white";

}

Now I want to derive another class Man out of it

to do so you need to write as following

Man.prototype.constructor = Man; //this line will tell that man object will be instantiated from its own prototype

Man.prototype = new Person; //this line will hook Person into Man's prototype chain

Please note that you have to write the above two lines before creating Man class

now I am writing a "Man" class

function Man()

{

this.color = "black";

}

just to explain you how you can add some properties/methods in objects prototype directly, you can refer following example

Person.prototype.legs = 4;

Man.prototype.legs = 2;

Man.prototype.hair = "black";

Ok, now I am going to create an object of Man class

var m = new Man(); //m is an object of Man

alert(m.color); // the interpreter will look into class Man first and will popup black

alert(Man.prototype.color); // since prototype of Man does not contain color property, it will move up the prototype chain and will look into Person prototype and popup "white"

alert(m.legs); //legs are not defined in object "m", it will look ito prototype of "m" and will pop up 2

I hope you must have understood by now how this whole inheritance is going to work. This is not different than how you find it working in C#/VB.Net or any other language.

Reference: http://aspnettechstuffs.blogspot.com/

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VB.Net to interop COM dll call failed for variant/object

March 29, 2008 10:22 by abhishek.tiwari

I converted one ASP application to VB.Net using Microsoft ASP migration assistant utility. It was interesting
to see that the utility created all the required interop dlls for my unmanaged COM components. so I saved my time in
running tlbimp on each COM/EXE/DLL(unmanaged) or by using Visual studio. Cool Eh!!
I found one very interesting and quite unexplored issue (atleast i didnot get much on googling ) that was my call from managed environment to unmanaged got failed for no obvious reason. Prima facie, I got feeling
that it happened due to some wrong marshalling of data which eventually proved true.

Let me staright jump into the issue by one example and explain its fix.

my backend (C++) has one API implementation something like this

CFoo::CreateMyList(

/*[in]*/ VARIANT* vSomeInVaiant,

/* [out] */ VARIANT* pvSomeOutVariant,

/* [in] */ BOOL bSomeBoolean,

BOOL* bRetVal )

my default VB.Net code (after conversion) was something like this,

blnRetVal = CFoo.CreateMyList(vSomeInVaiant, vSomeOutVariant, bSomeBoolean)

this call was ending up in some unhandled exception resulting a crash in application. To dig more I disassembled
my interop. I found the intermediate signature in my interop dll something like this

.method public hidebysig newslot abstract virtual

instance int32 CreateMyList([in] object marshal( struct) vSomeInVaiant,

[out] object& marshal( struct) pvSomeOutVariant,

[in] int32 bSomeBoolean,

) runtime managed internalcall

{

.custom instance void [mscorlib]System.Runtime.InteropServices.DispIdAttribute::.ctor(int32) = ( 01 00 03 00 00 00 00 00 )

} // end of method IFoo:::CreateMyList

when I hardcoded vSomeInVaiant in backend, everything worked fine. that meant the runtime marshaller is not able to do
his job properly for in variant. I donot owe to whatever fix I am going to tell you now.

I read it somewhere that by default VB.Net passes everything byref so I needed a way to pass it byVal. I found a workaround.
you enclose your variant (I'm sorry Object in managed env.) inside parantheses. that will make your runtime to evaluate it
as an expression first and then it will be forced to pass byVal.

the next thing i did was

blnRetVal = CFoo.CreateMyList((vSomeInVaiant), vSomeOutVariant, bSomeBoolean)

believe me the trick worked seamlessly. I applied this trick everywhere in my project and it worked.

To summarize it,

pass in variant enclosed in parantheses
pass out variant as it is
pass in/out variant ( never tried so far ), you need to let me know.

I am open to more discussion on this. I will be obliged for any comment.

Reference: http://aspnettechstuffs.blogspot.com/

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How to debug Javascript & ASP

March 24, 2008 02:21 by abhishek.tiwari

Writing alert in javascript and Response.Write in ASP to debug has been quite traditional. It just gives you an idea of the variable value runtime, what if

You want to frequently change the variable’s value on runtime to do some test
You want to step over or step into the function
There is a big variant (ASP) or object/Array (Javascript) and you just don’t know its dimension but want to see it all

There could be tons of reasons, you need a good debugging tool. I here tell you some simple tricks to ease your job.

Prerequisite: Microsoft Visual Interdev (comes with Microsoft Visual Studio 6.0)

Debug Javascript: By default, javascript debugging is disabled in browser. To enable it, Open IE, Go to

Tools -> Internet Options -> Advanced -> Browsing

Uncheck “Disable Script Debugging (Internet Explorer)”
Uncheck “Disable Script Debugging (Other)”
Check “Display a notification about every script error”
Uncheck “Show friendly HTTP Error Messages”

Now whichever line you want to start debugging with in Javascript, just write keyword debugger before that and run your page.

What will happen next: You will be prompted with an error (“A runtime error has been occurred, do you want to debug?”). Now click Yes and choose visual Interdev to debug. You will find interpreter halted on your “debugger” line. Now you can debug it as you debug any other language. Cool Eh!!!

Debug ASP: VBScript is generally preferred as server side language in ASP. Like javascript, vbscript debugging is by default off in IIS. To enable it, Type inetmgr on run prompt, (it will open your IIS (web server) config) Now browse to your app directory under IIS Right click Go To

Properties -> Configuration -> Debugging

Check “Enable ASP server-side script debugging
Check “Enable ASP client-side script debugging

Now whichever line you want to start with, write keyword stop before that. Now run your page.

What will happen next: You will be prompted with an error (“A runtime error has been occurred, do you want to debug?”). Now click Yes and choose visual Interdev to debug and Bingo!!! You can debug your ASP code like anything.

Reference: http://aspnettechstuffs.blogspot.com/

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Inheritance in JavaScript

Inheritance in JavaScript

VB.Net to interop COM dll call failed for variant/object

VB.Net to interop COM dll call failed for variant/object

How to debug Javascript & ASP

How to debug Javascript & ASP