$('#<%= myTextBox.ClientID %>')

$('[id$=myTextBox]') // id which ends with the text 'myTextBox'

$('[id*=myTextBox]') // id which contains the text 'myTextBox'

<asp:TextBox runat="server" ID="myTextBox" CssClass="myclass" /> //add CssClass

$('.myclass') //selector

<asp:TextBox runat="server" ID="myTextBox" ClientIDMode="Static"  /> //add ClientIDMode

$('#myTextBox') //use the normal ID selector

<asp:TextBox ID="txtSalesInvoiceDate" runat="server" />

var invDate = $("input[name=txtSalesInvoiceDate]");