Question

I posted a topic yesterday where a fella made a comment: How to use $_GET path with file_exists and keep it safe? stating that I’d get “undefined” returned due to JSON being asynchronous. He was right and I’ve been trying to wrap my head around why, but I feel completely out of my depth. I wonder if someone could explain just what’s happening so I can figure out how to use Deferreds to solve this or if there’s another solution.

Any help appreciated, cheers!

Answer 1

You code is

function fileExists(path){
    $.getJSON("/ajax/fileExists.php",{ path: path },
    function (data){
        return data.path;
    });
}

The problem here is that the inner function is a callback and the return inside will be executed after the Ajax request. At this time the outer function fileExists has already finished. It only started the request and does not wait for it to end.

To fix this you can make a callback

function fileExists(path, callback){
    $.getJSON("/ajax/fileExists.php",{ path: path },
    function (data){
        callback(data.path);
    });
}

Use it like this

fileExists('/a/path', function(path){ console.log(path) } );