Return NULL JavaScript

Question

I don't understand why I am getting alert "Empty" when I type some numbers or leave a empty? Can you help me?

My Code:

    </script> 

               <script type="text/javascript">
                   function tell() {
                       var v = true;
                       if (document.getElementsByName("TextBox33").length == 0)
                       alert("Empty");
                           v = false;

                       return v;
                   }
</script>

<asp:LinkButton ID="LinkButton1" runat="server" CausesValidation="True" CommandName="Insert" OnClientClick="javaScript: return tell();"

<asp:TextBox ID="TextBox33" onkeypress="return isNumberKey(event)" runat="server" Text='<%# Bind("imei") %>'></asp:TextBox>

I am adding more html:

<asp:DetailsView ID="DetailsView1" runat="server" DefaultMode="Insert" AutoGenerateRows="False" DataKeyNames="id" DataSourceID="SqlDataSource1" Height="50px" Width="286px" OnItemInserting="DetailsView1_ItemInserting" OnDataBound="DetailsView1_DataBound" OnItemInserted="DetailsView1_ItemInserted">

        <asp:TemplateField HeaderText="IMEI" SortExpression="imei">
            <EditItemTemplate>
                <asp:TextBox ID="TextBox3" runat="server" Text='<%# Bind("imei") %>'></asp:TextBox>
            </EditItemTemplate>
            <InsertItemTemplate>
                <asp:TextBox ID="TextBox33" onkeypress="return isNumberKey(event)" CssClass="TextBox33" runat="server" Text='<%# Bind("imei") %>'></asp:TextBox>
            </InsertItemTemplate>
            <ItemTemplate>
                <asp:Label ID="Label4" runat="server" Text='<%# Bind("imei") %>'></asp:Label>
            </ItemTemplate>
        </asp:TemplateField>

GetElementsByName returns a collection. It's empty not the TextBox. — Tony Hopkinson
– Tony Hopkinson, Commented Mar 21, 2015 at 14:25

Leah Sapan · Accepted Answer · 2015-03-21 14:34:05Z

2

You're calling getElementsByName which returns al array of DOM elements. You're then taking the length of that, which will always be more than 0 because the element exists.

Try adding a [0] after the getElementsByName call, and then change .text to .value.

Also so you're aware, you need to put the alert and v = false inside brackets. You can only skip brackets if you're executing one statement.

Here's the revised code:

if (document.getElementById("TextBox33").value.length == 0){
    alert("Oh no I'm empty!");
    v = false;
}

Update: I also just noticed that you didn't actually give the textbox a name of TextBox33, you gave it an ID. I've updated the code.

edited Mar 21, 2015 at 14:34

answered Mar 21, 2015 at 14:26

Leah Sapan

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10 Comments

Leah Sapan Over a year ago

Sure, I added it to the answer.

Myk Syk Over a year ago

I have got error: 0x800a138f - JavaScript runtime error: Unable to get property 'value' of undefined or null reference

Leah Sapan Over a year ago

My bad, I'm typing on a phone. I had ID in all caps, it's Id. Try now.

Myk Syk Over a year ago

Yes, Luke, I have tried with ID, but the problem is same and I don't know why... 0x800a138f - JavaScript runtime error: Unable to get property 'value' of undefined or null reference

Myk Syk Over a year ago

Yes. document.getElementById("TextBox33").value.length == 0

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