Is there a javascript client-side library for queuing ajax requests with storage support

Question

I'm looking for a javascript client side lib to handle an ajax or websocket requests queue like this :

• directly transmit request when user is online and the server is up
• store requests when user is offline or server is down using local storage
• send stored requests when user is online and server is back online

Ideally :

• without jquery
• I'm also looking for a serverside component to go along

I can't find anything like this. Should I build one myself using localstorage, window.navigator.onLine and socket.io for instance or is there already some lib for that purpose ?

Thanks.

Answer 1

The question is probably going to be closed, since asking for a library is usually not welcomed on StackOverflow. However, this is a fun little challenge. (Took me ~15 minutes to complete.)

This is actually not a very big task to handle, barely 50 lines or so. That's probably why you can't find a small library doing this.

function Sender() {
    var requests = [],
        state = 0; // 0 = closed, 1 = open
        ws = new WebSocket();

    ws.onopen = function() {
        state = 1;
        if (requests.length) {
            send();
        }
    };

    ws.onerror = function() {
        if (ws.readyState !== 1) { // 1 is "OPEN"
            close();
        }
    };

    // Let's fill in the requests array if necessary
    // IIFE because I don't want to pollute the scope with `req`
    (function() {
        var req = JSON.parse(localStorage.get('queue'));
        if (req.length) {
            requests = requests.concat(req);
        }
    }());

    return {
        send: function(msg) {
            if (state === 0) {
                requests.push(msg);
            }
            else {
                send();
            }
        },
        close: function() {
            state = 0;
            localStorage.set('queue', JSON.stringify(requests));
        }
    };

    function send() {
        var done = false;
        while (!done) {
            if (state === 1) {
                ws.send(requests.pop());
                if (!requests.length) {
                    done = true;
                }
            }
            else {
                done = true;
            }
        }
    }
}

// Usage example
var sender = Sender();
sender.send('message');

// let's say your "disconnect" button is in a variable
disconnect.addEventListener('click', function() {
    sender.close();
}, false);

The server doesn't have to handle anything except normal requests. If you want, you can add a timestamp to the message you send, this way it's quite easy (2 lines or so) to keep track of the time.