Auto triggering the change event

HTML

<textarea id="inptxt" ></textarea>
<div id="res" ></div>
<input type="button" value="click" id="but" />

JavaScript

$("#inptxt").on("change input paste keyup textarea", function() {
   $("#res").html(jQuery(this).val());
});
$("#but").bind("click",function(){
    $("#inptxt").val("Jquery not trigger the change function");
});