Javascript script to change the source of an image

I am using flexigrid for one of my projects and I need to come up with a way to change the image source depending on the value of one of the cells. For people who are used to flexigrid, I have the following code:

$json .= ",'".addslashes("<span><img src='' id='flag' />" . $row['availability']. "</span>")."'"; 

and my javascript that I've come up with , looks like this:

<script type="text/javascript"> 
var available = "<?php echo '$row[availability]' ?>"; 

if开发者_如何转开发 (available == 0) { 
document.getElementById('flag').src="images/flag_red.png"; 
} 
elseif (available == 1) { 
document.getElementById('flag').src="images/flag_green.png"; 
} 
else { 
document.getElementById('flag').src="images/flag_orange.png"; 
}

I am not sure where I need to insert this function and how to trigger it. Any help will be greatly appreciated.

Regards, Cristian.

LE: The code where the problem is being reported:

url: 'post2.php',
            dataType: 'json',
            colModel : [
                {display: 'ID', name : 'id', width : 40, sortable : true, align: 'center', hide: true},
                {display: 'URL', name : 'url', width : 450, sortable : false, align: 'left'},
                {display: 'File Name', name : 'filename', width : 270, sortable : true, align: 'left'},
                {display: 'Availability', name : 'availability', width : 50, sortable : true, align: 'center'},
                {display: 'State', name : 'state', width : 40, sortable : true, align: 'center'},
                {display: 'Total Size', name : 'totalsize', width : 90, sortable : false, align: 'center'},
                {display: 'Current Size', name : 'currentsize', width : 90, sortable : false, align: 'center'},
                {display: 'Procent', name : 'procent', width : 40, sortable : true, align: 'center'},
                {display: 'Log',  width : 20, sortable : false, align: 'center'},
                ],
            buttons : [
                {name: 'Add', bclass: 'add', onpress : test},
                {separator: true},
                {name: 'Delete', bclass: 'delete', onpress : test},
                {separator: true},
                {name: 'Select All', bclass : 'selectall', onpress : test},
                {name: 'DeSelect All', bclass : 'deselectall', onpress : test},
                {separator: true}
                ],
            searchitems : [
                {display: 'URL', name : 'url'},
                {display: 'Filename', name : 'filename', isdefault: true}
                ],
            sortname: "state",
            sortorder: "asc",
            usepager: true,
            title: '',
            useRp: false,
            rp: 5,
            showTableToggleBtn: true,
            } ----- **IE says there is a problem here**         );   
});

You shouldn't use javascript for this, you can do it directly in your existing PHP line.

$json .= ",'" . 
         addslashes("<span><img src='" . 
         ($row['availability'] == 0 ? "images/flag_red.png" :
            ($row['availability'] == 1 ? "images/flag_green.png" : 
               "images/flag_orange.png")
         ) . 
         "' id='flag' />" . $row['availability'] . "</span>") . "'";