调用上的函数更改 Textbox事件，而不是 document.ready ：

Call the function onchange event of Textbox as, instead of document.ready:

HTML

<asp:TextBox ID="txt" runat="server" onchange="onlyNum()"></asp:TextBox>

JQuery

    function onlyNum() {
      var $this = $('#txt');
      $this.val($this.val().replace(/\D/g, ''));
    }