Node.js async.whilst

var async = require('async');

var before = Date.now();

async.whilst(always, gameloop, stop);

function always() { return true; }

function gameloop(next)
{
    var after = Date.now();
    var dt = after - before;
    if (dt >= 500)
    {
        console.log("yipee!");
        before = after;
    }
    process.nextTick(next);
}

function stop()
{
    console.log("loop has stopped for some reason when it shouldn't")
}