fan_in

// the helper
function fan_in(target_count, final_callback)
{
    var values = [];
    var count = 0;
    return function(cur_value) {
        values.push(cur_value);
        if (++count == target_count)
            final_callback(values);
    };
}

// a function that does some work asyncly
function work_func(url, callback)
    $.ajax(url, {success: callback});
}

// what you want to do with all the results
function final_func(values)
{
    console.log("all the things:");
    console.log(values.join("\n"));
}

// how to use it
var fan_in_callback = fan_in(8, final_func);
for (var i = 0; i < 8; i++)
    work_func("http://stuff/" + i.toString(), fan_in_callback);