How to pass value from Asp.Net for JavaScript

Question

How write x and y in my TextBox , I write this but not Work

 <script language="javascript" type="text/javaScript">
     function PantallaResolucion()
     {
         var x = screen.width.toString();
         var y = screen.height.toString();
         var xx = document.getElementById("HiddenField1");
         var yy = document.getElementById("HiddenField2");
         xx.value = x;
         yy.value = y;
     }
</script>

my asp.net code

<asp:HiddenField ID="HiddenField1" runat="server" />
<asp:HiddenField ID="HiddenField2" runat="server"  />

C# code

protected void Page_Load(object sender, EventArgs e)
{
    string c = "<script language='javascript'> PantallaResolucion(); </script> ";
    ClientScript.RegisterStartupScript(this.GetType(), "PantallaResolucion();", c);
    TextBox1.Text = HiddenField1.Value.ToString() + "x" + HiddenField2.Value.ToString();// NOT WORK**
}

This code will not work. You messed up server side and client side logic. You have to right all this code on client side using javascript: function PantallaResolucion() { .... } PantallaResolucion(); document.getElementById("text1").val = x+y or smth like this — Alena Kastsiukavets
– Alena Kastsiukavets, Commented Jul 19, 2016 at 21:17

Christos · Accepted Answer · 2016-07-19 21:33:36Z

You could try the following:

var xx = document.getElementById("<%= HiddenField1.ClientID%>");
var yy = document.getElementById("<%= HiddenField2.ClientID%>");

You could take a look here to see an very detailed explanation about why this is needed. According to this link, in a few words:

When a Web server control is rendered as an HTML element, the id attribute of the HTML element is set to the value of the ClientID property. The ClientID value is often used to access the HTML element in client script by using the document.getElementById method.

A more clear approach to the whole problem it would be the following:

place this script at the bottom of your page, before the closing tag </body>

<script>
    function PantallaResolucion(){
        var width = screen.width.toString();
        var height = screen.height.toString();
        var hiddenFld1 = document.getElementById("<%= HiddenField1.ClientID%>");
        var hiddenFld2 = document.getElementById("<%= HiddenField2.ClientID%>");
        hiddenFld1.value = width;
        hiddenFld2.value = height;
        var textBox1 = document.getElemenetById("<%=TextBox1.ClientID%>");  
        textBox1.value =  hiddenFld1.value + "x" + hiddenFld2.value;
    }
</script>

Then clear the statements from the Page_Load method. By the way, I don't see any reason for having at all these two hidden inputs. You could delete them and make the corresponding changes to the the above script.

you misunderstood the question, value must be passed from Javascript to Asp.net
@AlenaKastsiukavets If I am not wrong, the OP, argues that a javascript script doesn't work. This script runs on the client and not on the server. Furthermore, I don't see an attempt to pass any value form the client to the server (js to asp.net). Correct?
As understood the goal is to calculate some value from hidden inputs in text field, it must be done fully on client side, if add var text = document.getElementById("<%= TextBox1.ClientID%>"); text.val = x + y; then we get the desired behavior I believe
@AlenaKastsiukavets I read again the whole question and I pointed out that you mentioned. So I edited my answer. Thank you !

Alena Kastsiukavets · Accepted Answer · 2016-07-19 21:34:01Z

1

Ok, there are no need for server side logic. You can do all on client side:

<script language="javascript" type="text/javaScript">
    var text = document.getElementById("<%= TextBox1.ClientID%>"); 
    var x = screen.width.toString();
    var y = screen.height.toString();
    text.value = x + ' ' + y;
</script>

I believe it is what you want

answered Jul 19, 2016 at 21:34

Alena Kastsiukavets

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