index.js

var Queue = function(parts) {
  var index = 0;
	
	this.read = function() {
		var part = parts[index];
		index++;		
		return part;
	};
	this.next = function() {
		var thiz = this;
		this.function(this.read(), function() {
			// pass in a conditionally recursive callback
			thiz.length() && thiz.next();
		});
	};
	this.length = function() {
		return parts.length - index;
	};
	this.push = function(arr) {
		[].push.apply(parts, arr);
	};
	this.go = this.next;
};

// queue up a list for asychronous `mapping`
var queue = new Queue([1,2,3,4,5]);
queue.function = function(part, cb) {
	send(part, function() {
		// iterate
		cb();
	});
};
queue.go();