What does the "?" mean in this?

[Al Smith]

Hi,
In the code below, what does the question mark do in the lines var keyCode... and var filter...?

var isNN = (navigator.appName.indexOf("Netscape")!=-1);

function autoTab(input,len, e) {
   var keyCode = (isNN) ? e.which : e.keyCode; 
   var filter = (isNN) ? [0,8,9] : [0,8,9,16,17,18,37,38,39,40,46];
   if(input.value.length >= len && !containsElement(filter,keyCode)) {
   input.value = input.value.slice(0, len);
   input.form[(getIndex(input)+1) % input.form.length].focus();
   }

Thanks,
Al.

[techgnome]

I can answer part of it.... For starters, it's JAvascript -- wasn't sure you got that or not.
"var isNN" and "var keycode" and "var filter" are variable declarations.
The funk stuff after the "=" is something known as "regular expresssions".... I believe in this case that it is checking for valid data entries.

[mendhak]

var keyCode = (isNN) ? e.which : e.keyCode;


It's the same as saying:

If (isNN) is true, then keyCOde = e.which
otherwise
if (isNN) is false, then keyCode = e.keycode

It's just a shortcut method for that


HTH

[Al Smith]

Hi,
Thanks for the reply.
I kind of understand JavaScript, e.g. var's, but I'm unfamiliar with a question mark in the variable declaration. I found something that mentioned a "switch" or "condition" but this didn't mean anything to me.
The above code came from a JavaScript AutoTab function. Here's the complete code.

<SCRIPT LANGUAGE="JavaScript">

var isNN = (navigator.appName.indexOf("Netscape")!=-1);

function autoTab(input,len, e) {
   var keyCode = (isNN) ? e.which : e.keyCode; 
   var filter = (isNN) ? [0,8,9] : [0,8,9,16,17,18,37,38,39,40,46];
   if(input.value.length >= len && !containsElement(filter,keyCode)) {
   input.value = input.value.slice(0, len);
   input.form[(getIndex(input)+1) % input.form.length].focus();
   }

   function containsElement(arr, ele) {
   var found = false, index = 0;
   while(!found && index < arr.length)
   if(arr[index] == ele)
   found = true;
   else
   index++;
   return found;
   }

   function getIndex(input) {
   var index = -1, i = 0, found = false;
   while (i < input.form.length && index == -1)
   if (input.form[i] == input)index = i;
   else i++;
   return index;
   }
return true;
}

</script>

The HTML uses onKeyUp="return autoTab(this, 2, event); in the input box.

Thanks,
Al.

[Al Smith]

Thanks mendhak.
Al.

[ccoder]

Originally posted by Al Smith
I kind of understand JavaScript, e.g. var's, but I'm unfamiliar with a question mark in the variable declaration. I found something that mentioned a "switch" or "condition" but this didn't mean anything to me.

You can declare and initialize variables in the same statement.
var keyCode = (isNN) ? e.which : e.keyCode; is just a shortcut for:
var keyCode;
keyCode = (isNN) ? e.which : e.keyCode;

isNN is the condition.

BTW, this type of statement can also be found in Java and C. It is sometimes called a ternary, most likely due to the 3 expressions that make up the entire expression: (expr1) ? expr2 : expr3.

[CornedBee]

BTW, there are no regular expressions in that code.

?: is the "conditional operator", and it is a ternary operator. This means it operates on three operands as opposed to binary (2 operands) or unary (1 operand) operators.