On typing finished jQuery plugin

If you are developing a form and you require certain validations; check if username is available or not for example - the way to do that is to listen for the change/focusout DOM events. You can also check it on every keypress but if the validation does some expensive checking in the background that is out of the question. So here is a really small jQuery plugin that does tell you when a user finished typing inside a text box. The way it does it is to compute the speed the user is typing with and when a delay longer than twice the speed average occurs, the event is triggered and your validation function is called. Simple enough.

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$(document).ready(function () {
  $.fn.onTypeFinished = function(func) {
     var T = undefined, S = 0, D = 1000;
     $(this).bind("keypress", onKeyPress).bind("focusout", onTimeOut);
     function onKeyPress() {
        clearTimeout(T);
        if (S == 0) { S = new Date().getTime(); D = 1000; T = setTimeout(onTimeOut, 1000); return; }
        var t = new Date().getTime();
        D = (D + (t - S)) / 2; S = t; T = setTimeout(onTimeOut, D * 2);
     }
 
      function onTimeOut() {
           func.apply(); S = 0;
      }
      return this;
   };
});

The way to use it:

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$("input[name='username']").onTypeFinished(myValidationFunction)

And here is a small demo:

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