How to get element by id in ASP.NET?

Question

I tried all the possible solutions to get the value of an element by id, but it did not work. I am using ASP.NET, I have searched for the controls and I know that the server changes the id of the TextBox1, so we use the clientID. But when I write console.log(data1), I get nothing or empty space.

var data1 = document.getElementById('MainContent_TextBox1').textContent;
var data1 = document.getElementById("<%=MainContent_TextBox1.ClientID %>").value; 

This is the ASPX code:

<asp:TextBox ID="TextBox1" runat="server" ></asp:TextBox>

And this the JS code:

 var data1 = document.getElementById('MainContent_TextBox1').textContent;

In the console, I get this error:

Uncaught SyntaxError: Unexpected end of input and its reference in the master file!

console.log(data1); appears in the console as empty place.

If anyone knows another way or why it is not working, please tell me.

Answer 1

Id of server controls gets changed and is appended with content place holder id so a very easy solution is to set a property ClientIDMode="static" on server controls. By setting this id of control will remain same and will not get changed so you will find it by getElementById in javascript.

<asp:TextBox ID="TextBox1" runat="server" ClientIDMode="static" ></asp:TextBox>

Answer 2

you can try like this to get master page control value in content page. document.getElementById('<%=Master.FindControl("Textbox1").ClientID %>'). If it's same page then you should be able to use directly document.getElementById("<%=TextBox1.ClientID %>").