hand：
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>
<script>
var N=1;
$(document).ready(function() {
$("#Do").click(function() {
N += 1;
$("#JYT").val("號碼" + N);
});

});
</script>

body：
<textarea style="width: 188; width:183; height:214; " rows="2" onfocus="this.focused=true;this.select();" onmouseup="if(this.focused){this.focused=false;return false;}" cols="20" id="JYT">
號碼1</textarea>
<div id="Do">點我</div>