How to return the response from an AJAX call

function foo() {
    var result;

    $.ajax({
        url: '...',
        success: function(response) {
            result = response;
            // return response; // tried that one as well
        }
    });

    return result;
}

var result = foo(); // always ends up being `undefined`.

this is a bad usage of AJAX. A function with an AJAX call never return anything. but instead hand off the data to something called a callback function, which handles the data. For example:

function handleData( responseData ) {
    // do what you want with the data
    console.log(responseData);
}

$.ajax({
    url: "hi.php",
    ...
    success: function ( data, status, XHR ) {
        handleData(data);
    }
});

Returning anything in the submit handler will not do anything, it must instead either hand off the data, or do what you want with it directly inside the success function.