Question

89

getElementById not finding control generated by ASP.net

rated 0 times [ 90] [ 1] / answers: 1 / hits: 72982 / 14 Years ago, tue, january 4, 2011, 12:00:00

I am simply trying to store a label in a variable in javascript but for some reason this isn't working with document.getElementById('control');. I know my javascript is linking to my html file fine because everything else works.

Here is my javascript code:

function performEvapCooledCircuit(txt)

{

    var error = document.getElementById('lblError');





    if (txt.value == null || isNaN(txt.value))

    {

       error.style.visibility = visible;

    }

}

Here is the html code for my label:

<asp:Label ID=lblError class=NormLabel runat=server 

   style=color:red; visibility:hidden; Text=Invalid Input.></asp:Label>

I am getting an error that says object expected??

Answers

Only authorized users can answer the question. Please sign in first, or register a free account.

ronans

Add To Favorites

Follow

Total Points: 460

Total Questions: 109

Total Answers: 108

Location: Slovenia

Member since Sat, Sep 11, 2021

3 Years ago

ronans questions

1 Warning: Accessing non-existent property 'sequelize' of module exports inside circular dependency

Tue, Jan 4, 22, 00:00, 2 Years ago

1 Cypress - Running only specific test cases from the test suite

Mon, Mar 29, 21, 00:00, 3 Years ago

1 How do I check two regex values with vuelidate

Sat, Oct 24, 20, 00:00, 4 Years ago

1 How to dynamically change SVG fill color?

Tue, Sep 15, 20, 00:00, 4 Years ago

1 How to make a div in a vue component take up the entire screen when using position absolute?

Fri, Jun 26, 20, 00:00, 4 Years ago

View All

answered 14 Years ago jordenfabiand · Accepted Answer

The ID that ASP.NET will generate will not be lblError so you'll need to reference it by its ClientID

document.getElementById('<%=lblError.ClientID %>');

If your javascript file is external I've usually had to write a type of Init javascript method to make sure my ID's were set up property

On your ASPX page:

<script type=text/javascript>

    var lblError = null;

    function InitializeVariables()

    {

        if (lblError == null) // make sure you only do this once

        {

            lblError = document.getElementById(<%=lblError.ClientID %>);

        }

    }

</script>

<asp:Label 

    ID=lblError

    class=NormLabel

    runat=server 

    style=color:red; visibility:hidden;

    Text=Invalid Input.></asp:Label>

Then in your javascript file you'll have to call InitializeVariables() to make sure you've got the variables pointing to the proper asp.net controls

function performEvapCooledCircuit(txt)

{

    InitializeVariables();



    if (txt.value == null || isNaN(txt.value))

    {

        lblError.style.visibility = visible;

    }

}