How do you serialize asynchronous activities in JavaScript?

You set an event handler on the object you're calling that returns asynchronously. There's really nothing you can do in javascript that's async without calling a method on some object -- timers are no exception. (When you call setTimeout, you're implicitly calling window.setTimeout.) So even if you could create a semaphore, or any other O/S synchronization object, it wouldn't be of any use because you can't create a thread.

An event handler is just a function, below is an example, using AJAX. In this example, the object req must be global so that it's visible inside of rscHandler.

// somewhere in global code...

var req = new XMLHttpRequest;

req.open("GET", url, true);

req.onreadystatechange = rscHandler;

req.send();

// ... script ends/returns control to host

function rscHandler() {

// handle event

if (req.status == 200) {

//...

}

}

btw, I'm not sure I follow your logic about timers, they work just fine if used correctly. If, by async activities you actually mean a single activity, from within which you want to yield the processor one or more times before it completes, timers are your only option, short of a Java applet or ActiveX.

"How does AJAX cut back the site visitors between the server and customer?" truly of fresh (resending) the entire web page (which could be hundreds of ok if there are portraits), AJAX facilitates you to deliver purely the request to the server, and get lower back purely the information to get replaced - which may be some bytes. for occasion, in a internet site that does unit conversions, you enter a length in inches. You click post. the information going to the server is the size you entered and, in all probability a single byte designating the gadgets to transform to and from. The server sends lower back a quantity, that's some bytes. (Javascript asynchronously gets that information and modifications the information in an ingredient on the web page to demonstrate it.)