I encountered a problem retrieving the value from a Textbox using its ID in JavaScript

When I have text boxes with values, I call my JavaScript method on one of the textboxes 'onblur'. The function looks like this:

function CalculateExpectedProductPrice() {
  alert("hi i called");
  var originalPrice = document.getElementById('hdnSelectedProductPrice').value;

  var numberOfLicenses = document.getElementById('txtNumberOfLicense').value;
  var enteredAmount = document.getElementById('txtAmount').value;

  alert(originalPrice);
  alert(numberOfLicenses);
  alert(enteredAmount);

}

I get an alert message saying "hi i called", but not further.

However, I am not getting the values of these controls for some reason.

*Updated:* Here is a snippet of my HTML code:

<asp:HiddenField ID="hdnSelectedProductPrice" runat="server" />
<asp:TextBox ID="txtAmount" runat="server" Width="250px"></asp:TextBox>
<asp:UpdatePanel ID="UpdatePanel2" runat="server" UpdateMode="Conditional">
   <ContentTemplate>
      <asp:TextBox ID="txtNumberOfLicense" runat="server" Width="35px" ></asp:TextBox>
   </ContentTemplate>
   <Triggers>
      <asp:AsyncPostBackTrigger ControlID="txtNumberOfLicense" EventName="" />
   </Triggers>
</asp:UpdatePanel>

Will there be any impact on the master-content page? The script and HTML are both on the same content page. Additionally, all these controls are part of the second step of a wizard control. Could this be causing the issue?

Updated:

I suspect that the wizard control might be causing the problem. Upon inspecting the generated HTML using Firebug, I noticed that IDs are assigned dynamically to controls inside the wizard. For example, the txtAmount textbox within the wizard control gets a name like:

ctl00_ContentPlaceHolder1_Wizard1_txtAmount

I would prefer not to use these generated IDs. Is there a way to find and set values for controls inside a wizard control without relying on these dynamic IDs?

Answer №1

Obtain the identification number of the control by following the steps below

var enteredAmount = document.getElementById('<%=txtAmount.ClientId%>').value;

Answer №2

It's difficult to determine without seeing your HTML code, but the common issue here is the confusion between the id and name attributes. While document.getElementById works with the id attribute, many people mistakenly believe it works with the name attribute on input fields (except in IE where getElementById does not function correctly).

(Also, remember that id values must be unique throughout the entire page, but based on the IDs mentioned, it seems like you are following this rule.)

Update: It will work if you use ids:

HTML:

<form>
  <input type='hidden' id='hdnSelectedProductPrice' value='10'>
  <input type='text' id='txtNumberOfLicense' value='2'>
  <input type='text' id='txtAmount' value='3'>
  <br><input type='button' id='theButton' value='Click Me'>
</form>

View live example

Answer №3

T.J. emphasized the importance of sharing your HTML code for us to provide accurate assistance. Without it, we might assume you are searching for specific element attributes.

Continue by identifying the element as you already have:

var element = document.getElementById('product');

Once you have the element, you can retrieve its attributes using:

var price = element.getAttribute('price');

Answer №4

In order to handle an "ASP.net server control", the following approach must be taken:

Let originalPrice = document.getElementById('<%=hdnSelectedProductPrice.ClientID %>').value;

Answer №5

When working with Asp.Net 4.0, and you have a unique textbox on the entire page, you can simply include ClientIDMode="Static" as an attribute of your textbox element.

<asp:TextBox ID="txtAmount" runat="server" Width="250px" ClientIDMode="Static"></asp:TextBox>

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