Node.js Serial Execution of an Async Function

control-flow-1.js

/* Control Flow 1 - Repetitive Serial Execution of an Asynchronous Function
 *
 * Based on:
 *   - http://book.mixu.net/node/ch7.html
 *   - https://github.com/mixu
 *
 * Revised to use "typeof(first_item) != 'undefined'" based upon comments from 'Israel'
 *
 * Characteristics:
 *   - Flow control construct 'series' is recursive
 *   - Runs a number of operations sequentially
 *   - Only starts one async operation at a time (no concurrency)
 *   - Ensures that the async function complete in order
 *
 * Variations:
 *   - The way in which the result is collected (manual or via a “stashing” callback)
 *   - How error handling is done (manually in each subfunction, or via a dedicated, additional function)
 *   - Since execution is sequential, there is no need for a “final” callback
 *
 * Tags: sequential, no-concurrency, no-concurrency-control
 */

/*
 * A Simulated Asynchronous Function
 */

function async(arg, callback) {
    var delay = Math.floor(1000 * Math.random());
    console.log('Do something with "' + arg + '", and return ' + delay + 'ms later');
    setTimeout(function() {
        result = arg; // Keep results same as argument so impact of async can be viewed
        callback(result);
    }, delay);
}

/*
 * A Simulated Completion Function
 */

function final(results) {
    console.log('Done', results);
    console.log(process.hrtime(start)[0] + "." + (process.hrtime(start)[1] / 1000000).toFixed(0) + " sec(s) total time");
}

/*
 * Recursive 'Series' Flow Control Construct
 */

function series(remaining_items, results) {
    var first_item = remaining_items.shift();
    if (typeof(first_item) != "undefined") {
        async(first_item, function(result) {
            results.push(result);
            console.log('Results so far: ', results);
            return series(remaining_items, results);
        });
    } else {
        return final(results);
    }
}

/*
 * Main
 */

var items   = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]; // Work array
var results = [];                              // Results array
var start   = process.hrtime();                // Start a timer

series(items, results);