javascript - AJAX polling and looping - Stack Overflow

admin管理员组

文章数量:1432177

My project is basically like a Reddit feed that updates in real-time. I'm trying to use AJAX to poll the server at intervals for updates on 15 items at a time.

I wrote a for loop but it caused the browser to lock up (I'm guessing too many XHRs?).

How can I poll each item on the Reddit-esque feed without locking up the browser? What is the most efficient way to do this?

Should I use long-polling if there are 100+ clients using the web app at the same time? Or should I opt for smart polling (increasing the wait time between requests if no data)?

Thanks! I'm still new to AJAX!

for (var i=0; i < id_array_len; i++) {
        // Grab current reply count

        var reply = $("#repl"+item_id).html();
        var url= *php function here*

        var ajaxRequest;

        try{
            // Opera 8.0+, Firefox, Safari
            ajaxRequest = new XMLHttpRequest();
        } catch (e){
            // Internet Explorer Browsers
            try{
                ajaxRequest = new ActiveXObject("Msxml2.XMLHTTP");
            } catch (e) {
                try{
                    ajaxRequest = new ActiveXObject("Microsoft.XMLHTTP");
                } catch (e){
                    // Something went wrong
                    alert("Your browser does not support AJAX!");
                    return false;
                }
            }
        }

        ajaxRequest.onreadystatechange = function(){
            if (ajaxRequest.readystate == 4){
                live_feed_data_tot = ajaxRequest.responseText;

                if (live_feed_data_tot.trim() == "no change" || live_feed_data_tot.trim() == "no meme" || live_feed_data_tot.trim() == "no response"){

                    console.log("(no update)");

                } else {

                    var live_feed_data = live_feed_data_tot.split(',');
                    if (live_feed_data[1] == 'reply') {
                        // Reply count has changed
                        new_reply = live_feed_data[0].trim();

                        // Update actual number
                        $("#repl"+item_id).html(new_reply);

                    }
                }
            }
        }

        ajaxRequest.open('POST', url, true);
        ajaxRequest.send();

My project is basically like a Reddit feed that updates in real-time. I'm trying to use AJAX to poll the server at intervals for updates on 15 items at a time.

I wrote a for loop but it caused the browser to lock up (I'm guessing too many XHRs?).

How can I poll each item on the Reddit-esque feed without locking up the browser? What is the most efficient way to do this?

Should I use long-polling if there are 100+ clients using the web app at the same time? Or should I opt for smart polling (increasing the wait time between requests if no data)?

Thanks! I'm still new to AJAX!

for (var i=0; i < id_array_len; i++) {
        // Grab current reply count

        var reply = $("#repl"+item_id).html();
        var url= *php function here*

        var ajaxRequest;

        try{
            // Opera 8.0+, Firefox, Safari
            ajaxRequest = new XMLHttpRequest();
        } catch (e){
            // Internet Explorer Browsers
            try{
                ajaxRequest = new ActiveXObject("Msxml2.XMLHTTP");
            } catch (e) {
                try{
                    ajaxRequest = new ActiveXObject("Microsoft.XMLHTTP");
                } catch (e){
                    // Something went wrong
                    alert("Your browser does not support AJAX!");
                    return false;
                }
            }
        }

        ajaxRequest.onreadystatechange = function(){
            if (ajaxRequest.readystate == 4){
                live_feed_data_tot = ajaxRequest.responseText;

                if (live_feed_data_tot.trim() == "no change" || live_feed_data_tot.trim() == "no meme" || live_feed_data_tot.trim() == "no response"){

                    console.log("(no update)");

                } else {

                    var live_feed_data = live_feed_data_tot.split(',');
                    if (live_feed_data[1] == 'reply') {
                        // Reply count has changed
                        new_reply = live_feed_data[0].trim();

                        // Update actual number
                        $("#repl"+item_id).html(new_reply);

                    }
                }
            }
        }

        ajaxRequest.open('POST', url, true);
        ajaxRequest.send();

• javascript
• ajax
• polling

Share Improve this question Follow edited Mar 21, 2012 at 19:29 Delos Chang asked Mar 21, 2012 at 19:09 Delos ChangDelos Chang 1,85333 gold badges3030 silver badges4747 bronze badges 2

• Show us the loop. I've done exactly this a few different times without locking up the browser so I expect it is something in your code. – Collin Green Commented Mar 21, 2012 at 19:17
• Added the code -- help would be much appreciated! – Delos Chang Commented Mar 21, 2012 at 19:29

Add a ment  | 

2 Answers 2

Sorted by: Reset to default 3

Use longpolling with a long (appropriate for your app of course) timeout. Your call needs to be asynchronous of course. As long as there is no data to deliver, the server holds the answer back, until the timeout is about to be reached. As soon as the client gets an answer, trigger the next longpoll in your plete()-Block. This way you can minimize the number of requests.

EDIT: after seeing your code i see you use native ajax but use jQuery for selecting. I suggest you to use jQuery for your ajax requests as well (jQuery .ajax() Doku).

Your code should look something like this:

function doAjaxLongpollingCall(){

   $.ajax({
     url: "...",
     timeout: <prettylong>,
     success: function(){
       //process your data
     },
     plete: function(){
       doAjaxLongpollingCall();
     }
   });
}

If you are doing a lot of users, switch to socket.io and save yourself the hassle. It uses websockets (which use a push mechanism) and does fallbacks to other mechanisms like flash sockets or long polling if thats not available in the browser. Requires you to create this piece of your app in node.js though.

本文标签： javascriptAJAX polling and loopingStack Overflow