CODEWITHSUNDEEP
javascriptjqueryajaxlong-polling
Ashwin Surana
Ashwin Surana

Reputation: 876

Efficient way to long poll in jquery

I am a beginner in javascript and jquery and was looking for an efficient way to long poll in jquery. I came across this piece of code and was puzzled by the attribute complete: . I am aware of the use of 'complete' but will this piece of code result in recursive function call? 

(function poll(){
    $.ajax({ url: "server", success: function(data){
        //Update your dashboard gauge
        salesGauge.setValue(data.value);

    }, dataType: "json", complete: poll, timeout: 30000 });
})();

Thanks in advance. :)

Upvotes: 1

Views: 439

Answers (2)

dcp3450
dcp3450

Reputation: 11187

To answer the OP question:

"complete: poll" will call the function again over and over. This would result in quite a bit of bandwidth, possible server timeouts, and if used by enough people could slow your server down.

Upvotes: 1

Platinum Azure
Platinum Azure

Reputation: 46183

You can avoid the recursion by using a short timeout to ensure that the current call stack clears:

(function poll(){
    $.ajax({
        url: "server",
        success: function(data){
            //Update your dashboard gauge
            salesGauge.setValue(data.value);
        },
        dataType: "json",
        complete: function () {
            setTimeout(poll, 0);
        },
        timeout: 30000
    });
})();

This will execute poll as (probably) the next event after the current execution clears. In other words, jQuery will execute the complete callback and return from everything until it's finally out of its onreadystatechange callback, at which point the JavaScript runtime will execute poll again (unless a different event came in and got onto the event queue first, of course).

Upvotes: 0

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