Wait until the test condition is true or a timeout occurs. Useful for waiting
on a server response or for a ui change (fadeIn, etc.) to occur.

@param testFx javascript condition that evaluates to a boolean,
it can be passed in as a string (e.g.: "1 == 1" or "$('#bar').is(':visible')" or
as a callback function.
@param onReady what to do when testFx condition is fulfilled,
it can be passed in as a string (e.g.: "1 == 1" or "$('#bar').is(':visible')" or
as a callback function.
@param timeOutMillis the max amount of time to wait. If not specified, 3 sec is used.
function waitFor(testFx, onReady, timeOutMillis) {
    var maxtimeOutMillis = timeOutMillis ? timeOutMillis : 3001, //< Default Max Timeout is 3s
        start = new Date().getTime(),
        condition = false,
        interval = setInterval(function() {
            if (new Date().getTime() - start < maxtimeOutMillis && !condition) {
                // If not time-out yet and condition not yet fulfilled
                condition =
                    typeof testFx === 'string' ? eval(testFx) : testFx(); //< defensive code
            } else {
                if (!condition) {
                    // If condition still not fulfilled (timeout but condition is 'false')
                    console.log("'waitFor()' timeout");
                    phantom.exit(1);
                } else {
                    // Condition fulfilled (timeout and/or condition is 'true')
                    console.log(
                        "'waitFor()' finished in " +
                            (new Date().getTime() - start) +
                            'ms.'
                    );
                    typeof onReady === 'string' ? eval(onReady) : onReady(); //< Do what it's supposed to do once the condition is fulfilled
                    clearInterval(interval); //< Stop this interval
                }
            }
        }, 100); //< repeat check every 100ms
}