Asynchronous Serial iteration

eachAsync.js

function eachAsync(iter, list, delay) {
    var i = 0,
        stopped = false,
        fwhenDone;
    delay = delay || 0;

    function run() {
        iter(list[i], done);
    }
    function hold() {
        setTimeout(stopped ? hold : run, delay);
    }
    function done() {
        i++;
        if (i < list.length) {
            setTimeout(stopped ? hold : run, delay);
        } else if (fwhenDone) {
            fwhenDone();
        }
    }

    setTimeout(run, delay);

    return {
        stop: function () {
            stopped = true;
        },
        start: function () {
            stopped = false;
        },
        whenDone: function (f) {
            fwhenDone = f;
        }
    };
}

eachAsync.usage.js

var data = [...];

eachAsync(function (el, done){
    // ... do work
    
    done(); // this could be called async
}, data);

whileAsync

function whileAsync(iter, delay) {
    var stopped = false;
    delay = delay || 0;

    function run() {
        iter(next);
    }
    function next() {
        setTimeout(stopped ? next : run, delay);
    }

    setTimeout(run, delay);

    return {
        stop: function () {
            stopped = true;
        },
        start: function () {
            stopped = false;
        }
    };
}

whileAsync.usage.js

whileAsync(function (loop) {
    // ... do work
    
    if (condition) {
        loop();
    }
});