Saturday, February 16, 2008

Check File Existence, Javascript (Prototype)


If you're like me, you spend a lot of time using System.IO and can easily check for the existence of a file on the filesystem with a File.Exists(@"C:\spam\eggs.file")

It's a little surprising that I hadn't run into it before but a few weeks ago I needed that same functionality with javascript. I found a few things online and what works best is using AJAX to make a request and check the HTTP status for whether or not the request failed.  My approach was to use Prototype and something like this:

function checkForFile(imgName, displayHolder){
new Ajax.Request('Repo/' + imgName + '.jpg',
onSuccess: function(transport){
var response = transport.status || "no response text";
if(parseInt(response) == 200){
displayHolder.src = 'Repo/' + imgName + '.jpg';'block';
onFailure: function(){
displayHolder.src = 'Repo/NoImage.gif';'block';

Works like a charm.


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