handy for worker process stuff when you want to throttle the frequency of requests.

delayedIterator.js

function delayedIterator(array, interval, callback, done) {
    var index = 0;
    var iterator = function iterator() {
        setTimeout(function () {
            if(array[index]) {
                callback(array[index], index);
                index++;
                iterator();
            }
            else {
                done();
            }
        }, interval);
    };
    if(!array.isArray) {
        iterator();
    }
    else {
        console.error('ERROR: '+ array + ' is not an Array');
        return done();
    }
};

var list = ['A', 'B', 'C'];

delayedIterator(list, 5000, 
            function (item, index) {
                console.log('### item', item, 'index:', index);
            }, 
            function () {
                console.log('#### DONE!');
            });