Simple series execution for asynchronous functions.

asyncSeries.js

/*
 * Inspired by the async module, but only needing async.series, I decided to code something minimal.
 *
 * funcs is an array of functions taking a single argument (a callback). It is assumed that these functions
 * operate with/on data outside of the local scope. The functions thus form a series of steps. cb is a
 * a final callback, which is called if a function in the series is handed an error (zeroth argument of any
 * function in the series as per convention) or otherwise when all functions in the array have been called.
 * Functions are called in order, from zeroth element up.
 *
 * The original async.forEachSeries assembles other callback arguments into an array. This can be easily
 * engineered in, but I find that I almost never use that feature, so this function leaves it out. Finally,
 * the array passed into the function is emptied by the function. Again, this can be avoided easily, but
 * has never been necessary for me.
 */

function asyncSeries(funcs, cb) {
	function worker(err, funcs) {
		if (err || !funcs.length) {
			return cb(err);
		}

		return funcs.shift()(callNext);
	}

	function callNext(err) {
		return worker(err, funcs);
	}

	return worker(null, funcs);
}