CODE:

var queue = [];
 
queue[0] = function(callback) {
    async_task1(function(){
    	callback();
    });
};
 
queue[1] = function(callback) {
    async_task2(function(){
    	callback();
    });
};
 
queue[2] = function(callback) {
    async_task3(function(){
    	callback();
    });
};

var finished = function() {
    print('Finished!');
}
 
(function(callback) {
    if (queue.length > 0) {
        var self = arguments.callee;
        queue[0](function(){
            queue.shift();
            self(callback);
        });
    } else {
        callback();
    }
})(finished);