Question

I have an Ajax jquery function ($.post) that retrieves json data. One of the ways it gets executed is by keydown ($(‘#lkj’).keyup(function(event)) with a 250 ms delay. One problem however is that the data retrieved is not always up to date. Especially when the user has a high ping towards the server. When i for example type “test”, the jquery .post script will get (depending on my typing speed) executed between two to four times:

1. t
2. te
3. tes
4. test

Sometimes the instance containing “te” is slow and is last the complete and therefore overwrites the output written by the instance containing “test”. How do I prevent that?

Answer 1

One technique is using a sequence number with your request, and processing the output only if it matches the latest request sequence number.

For example:

var reqSeq = 0;

When making your $.post call:

reqSeq++;
$.post('yourserver.com/yoururl?data=X&seq='+reqSeq, function(data) {

    // convert from JSON etc..

    // check if this response is for the latest request, if not, ignore response.
    if(data.seqNum < reqSeq) return;

    // process the response

});