Javascript,doesn't show undefined number

Question

I've created a variable with keys and values which looks like:

var e = new Array();
e[0] = "Bitte";
e[1] = "Danke";

Besides this I added a line in the variable which shows a text when the number is undefined.

e[NaN] = "Change Settings"; 

So when the variable e is NaN ("undefined"), I want that he doesn't displays the Number of the variable e in the input. I tried to achieve this as you can see, but it won't function.

if (neuezahl = NaN) {
  document.getElementById("saveServer").value="";
} else {
  document.getElementById("saveServer").value=""+neuezahl+""; 
}

Answer 1

You have assigned neuzahl not compared it, aside that use the isNAN function:

if (isNAN(neuezahl))
{
   document.getElementById("saveServer").value="";
}
else 
{
   document.getElementById("saveServer").value=""+neuezahl+""; 
}

https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/isNaN

Answer 2

NaN can't be compared directly (it's not even equal to itself NaN === NaN ==> false). Use isNaN() to detect NaN:

if (isNaN(neuezahl)) {...}