iphone - Pattern for wrapping an Asynchronous JavaScript function to make it synchronous

Question

I'm working with a JavaScript API where most of the functions are asynchronous. The API is the WebKit JavaScript Database API which is a binding to a subset of functionality to manipulate SQLite3 databases. I understand the design decision to make things async as to not block and provide a responsive user interface. In my situation I know that my usage of the async API calls will execute fast. Since this is the case I'd like to provide my developers a cleaner and easier to use wrapper API that forces synchronous calls.

Here's the async call

db.executeSql(sqlStatement, function(result) {
  // do something with result
});

And here's what I'd like to be able to do

var result = dbWrapper.executeSql(sqlStatement);
// do something with result

Is there a design pattern/way to do this? A written or linked to code example is preferred. The target platform/broswer is Mobile Safari on the iPhone.

Thank you

Answer 1

Sorry, JavaScript does not provide the language primitives (eg. threads or coroutines) to make asynchronous things act synchronously or vice-versa.

You generally* get one thread of execution only, so you can't get a callback from a timer or XMLHttpRequest readystatechange until the stack of calls leading to the creation of the request has completely unravelled.

So in short, you can't really do it; the approach with nested closures on the WebKit page you linked is the only way I know of to make the code readable in this situation.

*: except in some obscure situations which wouldn't help you and are generally considered bugs