Question

I have a ViewBag that has no value. I am not even defining the ViewBag.SelectVale
in my controller so I would expect it to be a null value.

When I do the following in JQuery but does not work:

    if ('@ViewBag.SelectVale' == null){ 

     // do something

     }

What works instead is something like:

    if ('@ViewBag.SelectVale' == ""){ 

     // do something

     }

Answer 1

In the .NET framework null gets output as an empty string, so if you look at the actual javascript being sent to the browser, in the first case it will say:

if ('' == null)

… and in the second case it will say:

if ('' == "")

Most javascript programmers would tell you to just change your statement to:

if ('@ViewBag.SelectVale')

… because empty strings evaluate to false when they are treated as boolean values in javascript.

Or, since there doesn’t appear to be anything really dynamic happening here, try this:

@if(ViewBag.SelectVale == null) {
    <text>
        // do something in javascript.
    </text>
}

… which will avoid even outputting the “do something” javascript since you know when you are rendering the page that SelectVale is null.