wrappers._js

// Wrapping asynchronous functions 
// This wrapper is implemented with callbacks
// i is the index of the callback in the parameter list
// isFuture is a reserved parameter - do not pass it
function wrapper1(fn, i, isFuture) {
  return function wrapped() {
		var cb = arguments[i];
		if (!isFuture) console.log("WRAPPER1 BEFORE CALL: " + fn.name);
		if (cb == null) return wrapper1(fn.apply(this, arguments), 0, true);
		arguments[i] = function(err, result) {
			if (err) return cb(err);
			console.log("WRAPPER1 AFTER CALL: " + result);
			cb(null, result);
		}
		fn.apply(this, arguments);
	}
}

// Wrapping asynchronous functions 
// This wrapper is implemented as a streamline function
// It only works if the callback is the first arg.
function wrapper2(fn) {
	return function(_) {
		// remove _ from argument list
		var args = Array.prototype.slice.call(arguments, 1);
		console.log("WRAPPER2 BEFORE CALL: " + fn.name);
		// invoke with apply_, callback index is 0
		var ret = fn.apply_(_, this, args, 0);
		console.log("WRAPPER2 AFTER CALL: " + ret);
		return ret;
	}
}

// Our asynchronous test function
function test(_, message) {
	console.log("BEFORE TIMEOUT: " + message);
	setTimeout(_, 1000);
	console.log("AFTER TIMEOUT: " + message);
	return "done";
}

// Testing the wrappers
try {
	console.log("****************")
	console.log("testing without wrapper");
	var r = test(_, "hello");
	console.log("r=" + r);
	
	console.log("****************")
	console.log("testing wrapper1");
	var wrapped = wrapper1(test, 0);
	var r = wrapped(_, "hello");
	console.log("r=" + r);
	
	console.log("****************")
	console.log("testing wrapper2");
	var wrapped = wrapper2(test, 0);
	var r = wrapped(_, "hello");
	console.log("r=" + r);

	console.log("****************")
	console.log("testing wrapper1 with future");
	wrapped = wrapper1(test)
	var f = wrapped(null, "hello");
	var r = f(_);
	console.log("r=" + r);

	console.log("****************")
	console.log("testing wrapper2 with future");
	wrapped = wrapper2(test)
	var f = wrapped(null, "hello");
	var r = f(_);
	console.log("r=" + r);
} catch (ex) {
	console.log("EXCEPTION: " + ex);
}