Checking for Null value

[Amandeep Singh]

In my procject we are using Internet Explorer 6.

I have added a new code-

------------------------
if (document != null && document.title != null && document.title == "Entry Event Tracking"
&& aListOfAppLockInfo != null && aListOfAppLockInfo[aListOfAppLockInfo.length -1] != null &&
aListOfAppLockInfo[aListOfAppLockInfo.length -1].owner_type != null && aListOfAppLockInfo[aListOfAppLockInfo.length -1].owner_type != "SESSION"){
return true;
}
------------------------

aListOfAppLockInfo is an array. It hold's different object's. Each object's has their own properties.
So i need to check for property 'SESSION'.

Can anybody let me know, my above code is correct and it will never fail, even if there is any null value?
Any suggestions also to improve this code.

Thanks in Advance.

[Ove Lindström]

You have to put up a cross matrix and see if you have any holes in it and with all this in one line you might miss something.

I would suggest that you break it down to at least two different ifs, one for all terminating controls (all items that may not be null) and one for the check if value present.

[Amandeep Singh]

Thanks Ove for your reply.

As you have suggested to break it into one for checking null and other for checking value's.

Is this only for testing purpose you have asked me or to modify the original code also?

[Eric Pascarello]

try debugging it as mentioned

alert(document != null);
alert(document.title != null);
alert(document.title == "Entry Event Tracking"); 
alert(aListOfAppLockInfo != null);
alert(aListOfAppLockInfo[aListOfAppLockInfo.length -1] != null);
alert(aListOfAppLockInfo[aListOfAppLockInfo.length -1].owner_type != null); alert(aListOfAppLockInfo[aListOfAppLockInfo.length -1].owner_type != "SESSION");

See which one fails. When you find it, alert the values and see what is wrong.

Eric

[Amandeep Singh]

Thank you so much Eric for your reply.

Well i tested through alert's, it's all working as expected.

Now the question i do have which piece of code should i use?

----------------------------
if (document != null && document.title != null && document.title == "Entry Event Tracking"
&& aListOfAppLockInfo != null && aListOfAppLockInfo[aListOfAppLockInfo.length -1] != null &&
aListOfAppLockInfo[aListOfAppLockInfo.length -1].owner_type != null && aListOfAppLockInfo[aListOfAppLockInfo.length -1].owner_type != "SESSION"){
return true;
}
-----------------------------

OR

this cross matrix form

----------------------------
if (document != null && document.title != null
&& aListOfAppLockInfo != null && aListOfAppLockInfo[aListOfAppLockInfo.length -1] != null &&
aListOfAppLockInfo[aListOfAppLockInfo.length -1].owner_type != null ){
if (document.title == "Entry Event Tracking" && aListOfAppLockInfo[aListOfAppLockInfo.length -1].owner_type != "SESSION"){
return true;
}
}
-------------------------------

which one is less error prone?

[Eric Pascarello]

They do the same thing. Do what you like.

Eric

[Amandeep Singh]

Thanks Eric.