You could take advantage of JavaScript's auto coertion

var myElt = document.getElementById("MyInputText");
var myVar = myElt ? myElt.value : null; // ternary operator similar to VFP's Iif()

>>>>What could be wrong with the following javascript line?
>>>>
>>>>

>>>>var MyVar = document.getElementById("MyInputText").value;
>>>>

>>>>
>>>>I have nothing in the javascript but the above line and Alert() after this line.
>>>>If I comment the above line, the Alert() fires. Otherwise, Alert() never fires. So I think there is something wrong with the above line.
>>>>But what?
>>>
>>>Well, you need to first test if document.getElementById returns an object. So, I would use two lines and check for object first. You also need to be sure that the id you're passing matches the id of the element.
>>>
>>>https://developer.mozilla.org/en-US/docs/Web/API/Document/getElementById
>>
>>How do you check/test if document.getElementById returns an object?
>
>var myElement = ...
>if (myElement!=null)
> ....
>
>It is explained in the link.