Some condition waiter with no blocking ui with synchronious first condition call.

wait_for.js

/*
 example of use: wait for jQuery load for 5 sec
 wait_for(function (){
     return window.jQuery;
 }, function () {
     $('body').addClass('js');
 }, 5000);
*/

function wait_for (condition, callback, timeout, interval) {
	var interval = interval || 50,
		waiter_interval;

	(function waiter () {
		var condition_result;

		try {
			condition_result = condition();
		} catch (err) {
			// error handling
		}

		if (condition_result) {
			callback();
		} else {
			waiter_interval = setTimeout(waiter, interval);
		}
	}());

	// stop waiting
	if (timeout) {
		setTimeout(function () {
			clearInterval(waiter_interval);
		}, timeout);
	}
}