We have a display board that needs to update every second. The AJAX call to the server triggers a stored proc that is a pretty simple SELECT statement and it takes only milliseconds to execute.

Originally, from time to time because of network latency (or sunspots, or who knows what) this AJAX process would (occasionally, rarely) time out. By tweaking how we handle the timer and by setting the timeout to 0, we have it so it's now running stable and the timeout never happens... yet.

That being said, I'm still nervous that a timeout could still happen. And IF happens, the goal is that it would just keep going. Basically, ignore the timeout and just try again... forever. Nothing like MaxError, or RetryLimit, or TryCount, etc.

Here's what I have now:

setTimeout(function run() {
    // When the timer elapses, get the data from the server
    GetData();
    setTimeout(run, _refreshRate);
}, 1000);


function GetData() {
    //console.log("Attempting to obtain the data...");
    jQuery.ajax({
        url: "something.ashx",
        type: "GET",
        contentType: 'application/json; charset=utf-8',
        success: function(resultData) {
            //console.log("Got the data.");
            ParseJson(resultData);
            // show the last refresh date and time
            $('#refreshTime').html(GetDateTime());
        },
        error : function(xhr, textStatus, errorThrown) {
            if (textStatus == 'timeout') {
                //console.log("Timeout occured while getting data from the server.  Trying again.");
                // If a timeout happens, DON'T STOP. Just keep going forever.
                $.ajax(this);
                return;
            }
         },
         timeout: 0,
    });
}

Everything inside of ParseJson(resultData); works great. No issues there. And The timer is setup (I believe) so that it will wait until one GetData() is done before it tries to start another.

I believe that by setting the timeout to 0 that it means "don't ever time out."

My question is this:

Am I correctly handling the error for a timeout? I am using the selected answer in this thread as my guide:

What's the best way to retry an AJAX request on failure using jQuery?

But I don't need a retryLimit limit.

I've also looked at these threads:

How to make the Ajax call again in case Time out error occurs

ajax timeout callback function

I think I've boiled all the info down to a simple solution, but I would like some peer review. Is there a better way to do this?

We have a display board that needs to update every second. The AJAX call to the server triggers a stored proc that is a pretty simple SELECT statement and it takes only milliseconds to execute.

Originally, from time to time because of network latency (or sunspots, or who knows what) this AJAX process would (occasionally, rarely) time out. By tweaking how we handle the timer and by setting the timeout to 0, we have it so it's now running stable and the timeout never happens... yet.

That being said, I'm still nervous that a timeout could still happen. And IF happens, the goal is that it would just keep going. Basically, ignore the timeout and just try again... forever. Nothing like MaxError, or RetryLimit, or TryCount, etc.

Here's what I have now:

setTimeout(function run() {
    // When the timer elapses, get the data from the server
    GetData();
    setTimeout(run, _refreshRate);
}, 1000);


function GetData() {
    //console.log("Attempting to obtain the data...");
    jQuery.ajax({
        url: "something.ashx",
        type: "GET",
        contentType: 'application/json; charset=utf-8',
        success: function(resultData) {
            //console.log("Got the data.");
            ParseJson(resultData);
            // show the last refresh date and time
            $('#refreshTime').html(GetDateTime());
        },
        error : function(xhr, textStatus, errorThrown) {
            if (textStatus == 'timeout') {
                //console.log("Timeout occured while getting data from the server.  Trying again.");
                // If a timeout happens, DON'T STOP. Just keep going forever.
                $.ajax(this);
                return;
            }
         },
         timeout: 0,
    });
}

Everything inside of ParseJson(resultData); works great. No issues there. And The timer is setup (I believe) so that it will wait until one GetData() is done before it tries to start another.

I believe that by setting the timeout to 0 that it means "don't ever time out."

My question is this:

Am I correctly handling the error for a timeout? I am using the selected answer in this thread as my guide:

What's the best way to retry an AJAX request on failure using jQuery?

But I don't need a retryLimit limit.

I've also looked at these threads:

How to make the Ajax call again in case Time out error occurs

ajax timeout callback function

I think I've boiled all the info down to a simple solution, but I would like some peer review. Is there a better way to do this?

• javascript
• jquery
• ajax
• settimeout

• From what it looks like, it should already be happening. Your run function is set to execute every 1 second. And it's set outside the scope of your ajax call, so it shouldn't matter if your ajax call times out or not. Have you tried debugging this? – Matt Spinks Commented Dec 11, 2017 at 15:08
• Every second puts heavy load on server. You should really use websockets for doing this – charlietfl Commented Dec 11, 2017 at 15:21
• @MattSpinks - yes, a lot. After much trial and error we got to this point and now it seems to be stable. By that I mean, it no longer times out. At least, we let it run for hours and tested it heavily and it never timed out, which before it was doing every couple of minutes. So I THINK we are good. Mostly I'm just looking for any peer suggestions on how to improve, or if there are an potential gotchya's in this code. – Casey Crookston Commented Dec 11, 2017 at 15:27
• @charlietfl, thank you! I really appreciate the idea. I confess I had not thought of websockets, but that might be a better solution. The good news is that the SP that is run is seriously tiny. We ran all kinds of tests on it inside SQL Query Analyzer and Profiler, and the load on the database server is almost non-existent. So, question: How would websockets help lower the load on the web server? – Casey Crookston Commented Dec 11, 2017 at 15:30
• Ok great. I would probably change your mechanism to poll from inside your success and error functions, instead of in your run function. The reason for this is that, if there is any kind of network error, then your code won't be blindly sending off more requests, even though the last request hasn't returned yet. – Matt Spinks Commented Dec 11, 2017 at 15:31

2 Answers 2

I'd prefer a solution that only queued a new call when the current had pleted. something like..

function poll() {
  setTimeout(function () {
     GetData();
  }, 1000);
}

function GetData() {
    jQuery.ajax({
        url: "something.ashx",
        type: "GET",
        contentType: 'application/json; charset=utf-8',
        success: function(resultData) {
            //...
        },
        error : function(xhr, textStatus, errorThrown) {
            //...
        },
        plete: function() {
           poll();
        },
        timeout: 0,
    });
}

poll();

This way your calls will not risk overlapping anyway.

function GetData() {
    //console.log("Attempting to obtain the data...");
    jQuery.ajax({
        url: "something.ashx",
        type: "GET",
        contentType: 'application/json; charset=utf-8',
        success: function(resultData) {
            //console.log("Got the data.");
            ParseJson(resultData);
            // show the last refresh date and time
            $('#refreshTime').html(GetDateTime());
        },
        error : function(xhr, textStatus, errorThrown) {
            if (textStatus == 'timeout') {
                //console.log("Timeout occured while getting data from the server.  Trying again.");
                // If a timeout happens, DON'T STOP. Just keep going forever.
                $.ajax(this);
                return;
            }
         },
         timeout: 0,
    });
}

var myInterval = setInterval(getData, 1000)
// if you want to stop it elsewhere:
// clearInterval(myInterval)

Instead of timeout you could use setInterval