Question

Basically just looking to see if a particular txt file exists on the server, and if so, do further processing; however, I don’t think my recursion is correct, so can someone offer a few pointers – here’s what I have:

function fileExists(filename) {
    $.ajax({
        type: 'HEAD',
        url: 'http://www.example.com/system/'+filename+'.txt',
        success: function() {
            // Further processing if file exists
        },  
        error: function() {
            // File does not exists, run through function again-
            return arguments.callee(filename);
        }
    });
}

It’s pretty basic, there’s some processing before hand that actually creates the file; however the issue is it’s FTP-ed up to our domain, which means timing can vary by a few seconds, so basically I just want it to recheck until it sees that the file exists. I’ll modify it a little afterwards to control the stack, possibly setting a timeout of half a second or something, but I’m not that great with javascript, so I need a few pointers to make this recursive. Any help is GREATLY appreciated.

Answer 1

the issue is when you try to call fileExists again via arguments.callee(fileName), the scope of the error method isn’t what you think it is.

Just call fileExists.

The other you are going to have is that if your server is quick, you are going to be firing a ton of requests. You probably want to wait some time between requests. So make error contain

setTimeout(function(){
    console.log('trying again....'); // this won't work in IE, I *think*
    fileExists(filename);
}, 1000); // try again in a second

Finally, you should realize that the error callback only gets invoked if the server returns a 500. The 500 code usually means there was an error on your server. If a file doesn’t exist, you should probably return json to indicate the file doesn’t exist, and handle that case in your success callback.