Messy async handling of error conditions

messy-async-with-callbacks.js

function thisMightFail(callback, errback) {
	xhrGet('/result', callback, errback);
}

function recoverFromFailure(callback, errback) {
	recoverAsync(
		function(result) {
			if(callback) {
				try {
					callback(result);
				} catch(e) {
					// Ok, callback threw an exception, let's switch to errback
					// At least this will let the caller know that something went wrong.
					// But now, both the callback and errback will have been called, and
					// and the developer may not have accounted for that!
					errback(e);
				}
			}
		}
		function(error) {
			if(errback) {
				try {
					errback(error);
				} catch(ohnoes) {
					// What do we do now?!?
					// We could re-throw or not catch at all, but no one can catch
					// the exception because this is all asynchronous.
					// And now console.error has infiltrated deep into our code, too!
					console.error(ohnoes);
				}
			}
		},
	);
}

function getTheResult(callback, errback) {
	
	// Simulating the catch-and-recover behavior of try/catch
	thisMightFail(callback, function(e) {
		
		recoverFromFailure(callback, errback);

	});

}