Javascript variable null error?

Question

Hi there I found an error in my javascript code using firebug, 'b is null' and my images are not changing.What I am trying to implement is 3 images swapping eventually on a webpage but standalone at the moment.Currently nothing is happening with it and I have tested in 3 well known browsers.

Any help would be great

<script type="text/javascript">  
var ImageArr1 = new Array("banner1.jpg","banner2.jpg","banner3.jpg");
var ImageHolder1 = document.getElementById("photo");

function RotateImages(whichHolder,Start)
{
    var a = eval("ImageArr"+whichHolder);
    var b = eval("ImageHolder"+whichHolder);
    if(Start>=b.length)
        Start=0;
    b.src = a[Start];
    document.getElementById('slideNumber').textContent = "Slide "+(Start+1)+" of         "+ImageArr1.length;
    window.setTimeout("RotateImages("+whichHolder+","+(Start+1)+")",3500);
}

RotateImages(1,0);
</script>

possible duplicate of [Why does jQuery or a DOM method such as \`getElementByID\` not find the element?](http://stackoverflow.com/questions/14028959/why-does-jquery-or-a-dom-method-such-as-getelementbyid-not-find-the-element) -- since `b` is `null` you are accessing the element before it exists. — Felix Kling, Jan 10 '13 at 13:26
Also you really should use arrays instead of variable variables... it's the path to hell. — Felix Kling, Jan 10 '13 at 13:27
Why... WHY are you using eval?!?!?!? Even when not using an array you could use `var a = window['ImageArr' + whichHolder];` to get the global variable. — ThiefMaster, Jan 10 '13 at 13:27
sounds like there is no element with the id photo... can you post your html? — CodeMonkey, Jan 10 '13 at 13:27
@user1259076: Besides a couple of other problems in your code, it seems that you are executing it before the element exists. Please follow the link in my first comment. — Felix Kling, Jan 10 '13 at 13:37

score 0 · Accepted Answer · answered Jan 10 '13 at 13:26

0

Since you're using Start to index into a, you should probably change your if condition to reflect this:

...
if(Start>=a.length)
    Start=0;
...

answered Jan 10 '13 at 13:26

Jannik Jochem

1,456
1
14
28

Also a valid point, but does not solve the problem with `b` ;) – Felix Kling Jan 10 '13 at 13:29
– user1259076 Jan 10 '13 at 13:29

Javascript variable null error?

1 Answers1