Barcode vs keyboard input detection

Create Dynamic Action

when key press

Execute JavaScript 

var delay = (function(){

   var timer = 0;

   return function(callback, ms){

      clearTimeout (timer);

      timer = setTimeout(callback, ms);

   };

})();

$("#P101_TEST").on("input", function() {

   delay(function(){

      if ($("#P101_TEST").val().length < 8) {

          $("#P101_TEST").val("");

      }

   }, 50 );

}); 

fire on pageload no.

Example

https://apex.oracle.com/pls/apex/f?p=131188