You are dealing with an asynchronous function call here. Results are handled when they arrive, not when the function finishes running.

That's what callback functions are for. They are invoked when a result is available.

function get(url, callback) {

    var xhr = new XMLHttpRequest();

    xhr.open(GET, url, true);

    xhr.onreadystatechange = function () {

        if (xhr.readyState == 4) {

            // defensive check

            if (typeof callback === function) {

                // apply() sets the meaning of this in the callback

                callback.apply(xhr);

            }

        }

    };

    xhr.send();

}

// ----------------------------------------------------------------------------





var param = http://example.com/;                  /* do NOT use escape() */

var finalUrl = http://RESTfulAPI/info.json?url= + encodeURIComponent(param);



// get() completes immediately...

get(finalUrl,

    // ...however, this callback is invoked AFTER the response arrives

    function () {

        // this is the XHR object here!

        var resp  = JSON.parse(this.responseText);



        // now do something with resp

        alert(resp);

    }

);

Notes:

• escape() has been deprecated since forever. Don not use it, it does not work correctly. Use encodeURIComponent().


• You could make the send() call synchronous, by setting the async parameter of open() to false. This would result in your UI freezing while the request runs, and you don't want that.


• There are many libraries that have been designed to make Ajax requests easy and versatile. I suggest using one of them.