Wednesday 20 January 2016
How to fix error - JavaScript runtime error: Unable to set property 'className' of undefined or null reference
Watch this example on YouTube:
To illustrate the issue here are my components involved in it
1. CSS
.ShowForm{
border: 2px;
visibility: visible;
background-color: red;
width:100px;
top:200px;
height:100px;
left:100px;
}
.HideForm {
visibility:hidden;
}
2. Html
<%@ Page Language="vb" AutoEventWireup="false" CodeBehind="JavaScriptPopup.aspx.vb" Inherits="VBTest.JavaScriptPopup" %>
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
<link href="Styles/StyleSheet1.css" rel="stylesheet" />
</head>
<body>
<form id="form1" runat="server">
<div class="HideForm" id="showDiv">
</div>
<div><asp:LinkButton ID="LinkButton1" runat="server" OnClick="LinkButton1_Click" >Show Form</asp:LinkButton></div>
</form>
</body>
</html>
3.Code Behind
Public Class JavaScriptPopup
Inherits System.Web.UI.Page
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
End Sub
Protected Sub LinkButton1_Click(sender As Object, e As EventArgs) Handles LinkButton1.Click
Dim sbTest As New StringBuilder()
sbTest.Append("<script type=""text/javascript"">")
sbTest.Append("document.getElementById('showDIV').className='ShowForm';")
sbTest.Append("</script>")
Page.ClientScript.RegisterStartupScript(Page.[GetType](), "show me", sbTest.ToString(), False)
End Sub
End Class
to fix it replace
sbTest.Append("document.getElementById('showDIV').className='ShowForm';")
with
sbTest.Append("document.getElementById('showDiv').className='ShowForm';")
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