check value of text box

I normally program in php, but I need to check the value of a text box in javascript. I have the following code...

// JavaScript Document
function isZip(item)
{
    var item=item;
    alert(document.frmClaim.item.value);//to verify it has gotten the value
    var str=document.frmClaim.item.value;
    alert("yes");
    if(isNaN(str)){
        alert('That value must be a number.');
        document.frmClaim.item.focus();
        document.frmClaim.item.value = '';
        
    };
}

><input type="text" onblur="isZip('insured_zip')" size="7" maxlength="9" name="insured_zip" id="insured_zip" value="<?php echo $_POST['insured_zip']; ?>">

Code (markup):

 

it doesn't alert the yes or the value. I can alert item and it alerts insured_zip. Anyone have any ideas? Thanks!

 

and if I replace "item" with insured_zip it works. So basically I need help getting it to use insured_zip as the item.

 

Free JavaScript Code | HTML-JS-CSS Encoding | CSS Menus​

 

Try this.

Hope this helps,

 

Ok, I got it to check the value, but now I need it to set the focus back to the object if its not a number. I've tried 50 different things with that focus(). Any ideas?

 

just tried it in ie and it works fine. not in Mozilla/5.0 browser.