readylist

example.js

var ready = require('./ready');
var cdCache = {};

function getDiskData (discId) {

    cdCache[discId] = cdCache[discId] || ready(function (done) {
        setTimeout(function () {
            done(Math.random());
        }, 2000);
    });

    cdCache[discId].add(function () {
        console.log.call(this, arguments);
    });
}

setInterval(function () {
    getDiskData("10"); // 10 is a disc id
}, 500);

ready.js

module.exports = ready;

function ready (get) {
    var queue = [],
        results,
        state = 'waiting';

    function completeQueue () {
        while (queue.length > 0) {
            queue.shift().apply(null, results);
        }
    }

    return {
        add: function (done) {
            queue.push(done);
            if (state === 'waiting') {
                state = 'running';
                get(function () {
                    state = 'ready';
                    results = arguments;
                    completeQueue();
                });
            } else if (state == 'ready') {
                completeQueue();
            }
        }
    }
}