javascript - Accurate long polling example? - Stack Overflow

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I've made an function that should do an long polling and fetch live data that is being "pushed" to me. Right now I'm testing against an json object that is formatted in the way that it will look once I receive the data. It seems as it is working accurate so far. I was merely wondering what you think about it? Would you refactor it somehow or do it entirely in another way?

var url = '../../path_to_script/respondents.json';

function fetchData() {
  $.ajax({
    url: url,
    method: 'GET',
    dataType: 'json',
    contentType: "application/json; charset=utf-8",
    cache: false,
    success: function (data) {
        //parseData(data);
        setTimeout(function () { fetchData() }, 5000);
        console.log(data);
    },
    error: function (data) {
        setTimeout(function () { fetchData() }, 5000)
    }

 });

}

Regards

I've made an function that should do an long polling and fetch live data that is being "pushed" to me. Right now I'm testing against an json object that is formatted in the way that it will look once I receive the data. It seems as it is working accurate so far. I was merely wondering what you think about it? Would you refactor it somehow or do it entirely in another way?

var url = '../../path_to_script/respondents.json';

function fetchData() {
  $.ajax({
    url: url,
    method: 'GET',
    dataType: 'json',
    contentType: "application/json; charset=utf-8",
    cache: false,
    success: function (data) {
        //parseData(data);
        setTimeout(function () { fetchData() }, 5000);
        console.log(data);
    },
    error: function (data) {
        setTimeout(function () { fetchData() }, 5000)
    }

 });

}

Regards

• javascript
• jquery
• ajax
• json
• long-polling

Share Improve this question Follow asked May 5, 2011 at 7:18 TimTim 54122 gold badges77 silver badges2525 bronze badges

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3 Answers 3

Sorted by: Reset to default 3

This works like expected. Since you've wisely choosen to fire a setTimeout once the request returned, there can't be "overlapping" requests. That is a good thing.

Anyway, you could use jQuerys "new" deferred ajax objects which is probably a little bit more convinient.

(function _poll() {
    $.getJSON( url ).always(function( data ) {
        console.log( data );
        _poll();
    });
}());

Note: .always() is brandnew (jQuery 1.6).

Edit

Example: http://jsfiddle/rjgwW/6/

I suggest changing the events to:

success: function (data) {
    console.log(data);
},
plete: function () {
    setTimeout(function () { fetchData() }, 5000)
}

The plete event is always called after success and error. This way you will only have the setTimeout line once, which is better.

I would do some changes

• Change method to type, method isn't a valid parameter for $.ajax. This is an error
• Remove contentType, with dataType: 'json' is enough to have those values
• Do something when there's an error. Use the error parameters if you need them. For example:

.

error: function (xhr, status, errorThrown) {
  alert("There was an error processing your request.\nPlease try again.\nStatus: " + status);
}

Hope this helps. Cheers

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