javascript textbox1 is null

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Hi
I have a textbox with name txt1.

In javascript, I am making txt1 mandatory, but now I have a added dropdownlist.

So, now txt1 is mandatory only when, the specific value of dropdown is selected.

That means, when I select name from dropdown, then txt1 is mandatory and when I select class from dropdown the txt1 should set to visible off.

Now I make txt1 visible to false, when i select class in dropdown, but it is throwing javascript error that txt1 is null in following line.

But when I select name from dropdown then no error comes because it is visible.

JavaScript

if(document.getElementById('<%=Txt1.ClientID%>').value=="")

Posted 2-Aug-12 22:37pm

balongi

Updated 2-Aug-12 22:45pm

Tadit Dash (ତଡିତ୍ କୁମାର ଦାଶ)

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Tadit Dash (ତଡିତ୍ କୁମାର ଦାଶ) 3-Aug-12 4:47am

Please post the whole code...

efkah 3-Aug-12 5:17am

how do you set the visible style? and: whats the problem? you dont need it anyways;-) just write if (document.getElementById('bla') == null) instead!

enhzflep 3-Aug-12 5:21am

Well, two things I can think of that would make it fail are
1.) variable names are Case Sensitive. i.e txt1 and Txt1 are different vars
2.) If the textbox's name is txt1, you're not going to locate it by searching for an element that has the id of Txt1

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Christian Graus · Answer 1 · 2012-08-03T12:16:00

If you make it not visible in your ASP.NET code, then it won't be rendered. As such, it is indeed null, it is not there. I'm not sure why the other answerers are confused, it's obvious you're using ASP.NET from the code you posted, and that this is how it works.

Overall, you should always write code that checks if an object exists before accessing it. You should move towards using jquery, which would solve your issue ( it just doesn't return anything if the object is not found ), and move to ASP.NET MVC if you can, in the future.