Martin Cipriano Martin Cipriano - 5 months ago 13
Javascript Question

What is the proper way of doing long polling using jQuery and AJAX

I have a project which involves live notification. So I stumbled upon using socket io but I didn't have enough time to learn it yet. So I tried doing it with AJAX and jQuery. Below is my code structure and I was wondering if this is gonna work with no drawbacks?

setInterval(function(){
if( !element.hasClass('processing') ){
element.addClass('processing');
$.ajax({
type: 'post',
dataType: 'json',
url: ajaxurl,
data: {},
success: function( response ){
/* Success! */
element.removeClass('processing');
}
});
}
}, 2500);

Answer

Some Extra Info

The way you described will work. From Experience I would just like to point out some things.

  • I usually do a recursive function, allows you to wait your interval between ajax calls and not a fixed rate. //OPTIONAL BUT DOES GIVE THE SERVER SOME BREATHING ROOM.

  • Use window.setTimeout() with an isActive flag. //ALLOWS YOU TO STOP POLLING FOR WHATEVER REASON, AND BECAUSE FUNCTION IS RECURSIVE START UP AGAIN IF NEED BE

  • For Sake of being thorough, I found it is always a good idea to handle the error case of the $.ajax() post. You could perhaps display some message telling the user he is no longer connected to the internet etc.

Some Sample Code:

var isActive = true;

$().ready(function () {
    //EITHER USE A GLOBAL VAR OR PLACE VAR IN HIDDEN FIELD
    //IF FOR WHATEVER REASON YOU WANT TO STOP POLLING
    pollServer();
});

function pollServer()
{
    if (isActive)
    {
        window.setTimeout(function () {
            $.ajax({
                url: "...",
                type: "POST",
                success: function (result) {
                    //SUCCESS LOGIC
                    pollServer();
                },
                error: function () {
                    //ERROR HANDLING
                    pollServer();
                }});
        }, 2500);
    }
}

NOTE

This is just some things I picked up using the exact method you are using, It seems that Web Sockets could be the better option and I will be diving into that in the near future.