In relation to validation of text fields

Recently, I created a basic JavaScript function to validate textboxes on an ASPX page

     <body>
     <script type="text/javascript" > 
      function checkTextbox(sender, target) {

      if (document.getElementById(sender).value  < document.getElementById(target).value) {
            var lbl = document.getElementById('<%=lbl_Outlet_Message.ClientID %>');
            lbl.style.display = 'block';
            lbl.value = "Enter Slab To Value should be greater or equals to From Value ";
        }

    }
</script>
<form id="form1" runat="server">
 <asp:Label ID="lbl_Outlet_Message" runat="server" ForeColor="Red" Visible="False"></asp:Label>
 <asp:TextBox ID="txt_from_02" runat="server" ></asp:TextBox> 
<asp:TextBox ID="txt_to_02" runat="server" onKeyUp="checkTextbox(this,'txt_from_02')">
</asp:TextBox>

</form>
</body>

Upon running the ASPX page, I encountered the following error message: "0x800a01a8 - Microsoft JScript runtime error: Object required". Unfortunately, identifying where exactly I went wrong has been challenging.

Answer №1

When using the function checkTextbox, it expects the sender as an id. However, you are currently passing the current object using this. To correct this, you should use this.id instead of just this, or modify the if condition to directly assess the value property of the current object without passing it to document.getElementById

Change

if (document.getElementById(sender).value

To

if (sender.value

Answer №2

When using document.getElementById, it may not be able to locate the ASP.NET control if only an ID name is provided, leading to a null return value and potentially causing an exception to be thrown.

To avoid this issue, consider utilizing the clientID property instead.

Here's how you can make the necessary change:

<asp:TextBox ID="txt_to_02" runat="server" onKeyUp="checkTextbox(this,'txt_from_02')">

Update it to:

<asp:TextBox ID="txt_to_02" runat="server" onKeyUp="checkTextbox(this,'<%=txt_from_02.ClientId %>')">

Answer №3

It appears that you are using the document.getElementById function without passing the specific Id of the textbox. This is causing an error in your code. By passing the entire object of the textbox using "this", the actual id is not being retrieved by document.getElementById(sender). To resolve this issue, consider implementing the solution provided below:

<body>
 <script type="text/javascript" > 
  function checkTextbox(sender, target) {

  if (document.getElementById(sender.id).value  < document.getElementById(target).value) {
        var lbl = document.getElementById('<%=lbl_Outlet_Message.ClientID %>');
        lbl.style.display = 'block';
        lbl.value = "Enter Slab To Value should be greater or equals to From Value ";
    }

}

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