Async task list that starts to execute immediately as soon as you push it.

gistfile1.js

function Tasks(){
    var totalTasks = 0,
        tasksComplete = 0,
        taskResults = [],
        waiting = false,
        self = this;

    this.push = function(task){
        var taskId = totalTasks;
        totalTasks += 1;
        task(function(err, result){
            onTaskComplete(taskId, err, result);
        });
    };

    function onTaskComplete(taskId, err, result){
        taskResults[taskId] = { err: err, result: result };
        tasksComplete += 1;
        if(waiting && tasksComplete == totalTasks){
            onFinish();
        }
    }

    function onFinish(){
        self._onFinish(taskResults);
    }

    this.await = function(callback){
        self._onFinish = callback;
        if(tasksComplete == totalTasks){
            onFinish();
        } else {
            waiting = true;
        }
    };
}

var taskList = new Tasks();
taskList.push(function(callback){
    setTimeout(function(){ callback(null, 1); }, 100);
});

taskList.push(function(callback){
    setTimeout(function(){ callback(null, 2); }, 200);
});

taskList.await(function(results){
    console.log(results);
});

// Results: [ {err: null, result: 1}, { err: null, result: 2} ]