CODEWITHSUNDEEP
c#javascriptjqueryasp.net
Muhammad Akhtar
Muhammad Akhtar

Reputation: 52241

Executing JavaScript function in Code behind -- How to Get the Return Value in Code Behind

I have following JavaScript function, Which call Jquery JSON function and get the DateTime with respect to timezone. This works fine.

  <script type="text/javascript">
    function JSFunctionName() {
        $(document).ready(function () {
            var timezone = "US/Central";
            $.getJSON("http://json-time.appspot.com/time.json?tz=" + timezone + "&callback=?",
function (data) {
    if (data.hour < 12) {
        //alert(data.hour + ':' + data.minute); // want to return this value data.hour + data.minute
        //document.getElementById('<%=HiddenField1.ClientID %>').value = data.hour + ':' + data.minute;// this does not work
    }
})
        });
    }
</script>

Now I am calling this Javascription function in Code behind on onclick of button

<asp:Button ID="Button1" runat="server" Text="Button" onclick="Button1_Click" />

Code behind

protected void Button1_Click(object sender, EventArgs e)
{
    Page.ClientScript.RegisterStartupScript(this.GetType(),
        "alert", "JSFunctionName();", true);
    // here I need the DateTime value that is get from JSON
    //Response.Write(HiddenField1.Value); 
}

How can I return the value from Javascript to code behind immediate after call of Page.ClientScript.RegisterStartupScript

Please note I have try to set the value in HiddenField, but its not working. you can see in the comment.

Any idea or alternative solution will be appreciated.

Thanks

Upvotes: 1

Views: 7760

Answers (3)

Matt Hilton
Matt Hilton

Reputation: 111

Your problem is that the following line:

Page.ClientScript.RegisterStartupScript(this.GetType(),
    "alert", "JSFunctionName();", true);

doesn't actually "execute" the Javascript funciton. It just adds the

JSFunctionName();

to the page in a script block, to be executed after your code has completed, and the page has loaded.

Rather than "calling the Javascript" from your button-click event, you could set the "OnClientClick" property of the button to "JSFunctionName()":

<asp:Button ID="Button1" runat="server" Text="Button" 
    onclick="Button1_Click" OnClientClick="JSFunctionName();" />

This will cause the JSFunctionName to fire before the postback happens. You can then set up your JSFunctionName() method to return true when it's done, which will then fire the postback.

You will then be able to access the value of HiddenField1 from the server-side click handler.

Upvotes: 0

IUnknown
IUnknown

Reputation: 22448

You can use ajax call to server from the javascript function or you may put another button on the form, hide it with style and cause click on this button after you set up calculated value to the hidden field in the JSFunctionName function.

Upvotes: 0

Khanzor
Khanzor

Reputation: 5000

You can't do this without posting back to the server. The reason for this is that javascript executes on the client, and it will only execute after the page has left the server.

I assume this is a contrived example, but in this specific case, if you want to have the same information available on the client and server, you need to compute it on the server, and pass that out to the client.

If this isn't possible, you'll need to create a webservice, but that will have to handle the response asynchronously.

Upvotes: 1

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