Lightweight Asynchronous Error Handling for Node.js (LAEH)

The Evolution

1. Unprotected callback code

function someContext(arg, arg, callback) {

	callAsyncFunction(arg, arg, function(err, data) {
		// err is not checked but should be (a common case)
		throw new Error('fail'); // uncaught - will exit Node.js
	}

}

2. Manualy protected callback code, lots of clutter

function someContext(arg, arg, callback) {

	callAsyncFunction(arg, arg, function(err, data) {
		if(err)
			callback(err);
		else {
			try {
				throw new Error('fail');
			}
			catch(e) {
				callback(e); // caught - return control manually
			}
		}
	}

}

3. LAEH, an elegant solution

function someContext(arg, arg, callback) {

	callAsyncFunction(arg, arg, _x(function(err, data) {
		throw new Error('fail');
	},
	callback, // in case of error return control to callback
	true); // automatically check the err parameter

}

4. Optional Goodies

LAEH stores the stacktrace of the thread that initiated the asynchronous operation which in turn called the callback. This stacktrace is then appended to the primary stacktrace of the error which happened in the callback, or the error which was passed to the callback by the asynchronous function.

LAEH then presents the stacktrace in a minified format, with optional hiding of frames of the laeh.js itself, of the node.js core library, shortens the often repeating string /node_modules/ into /$/, and removes the current directory path prefix from the file names in the stacktrace.

Usage

npm install laeh

var laeh = require('laeh').leanStacks(true, '\t');
var _e = laeh._e;
var _x = laeh._x;

The leanStacks(hiding, prettyMeta) call is optional, the hiding will hide stack frames from Node's core .js files and from laeh.js itself. The prettyMeta is the third parameter for the JSON.stringify function, which is used to serialize your metadata objects (see below), and leaving it empty will serialize your metadata objects in-line.

The _e(err, meta) function is just a convenient error checking, wrapping and throwing. E.g. _e('something') will throw new Error('something') and _e(null) will not do anything. The meta parameter is an optional accompanying information for the error to be thrown, which is then displayed when you let LAEH to display your errors using the leanStacks() call.

In the _x(func, cb, chk), the func is you callback to be wrapped. If it follows the node convention of func(err, args), you can pass chk as true, which will automatically check for the err to be null, and call the eventual callback if it isn't null. The eventual callback is passed as the cb argument, or if omitted, it is tried to be derived from the last argument parseed to the function you are wrapping, e.g. if the signature is func(err, args, cb), the cb is taken.