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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

share|improve this question
 
Are you using updatepanels? In that case the $(document).ready event probably won't fire after the button click event. –  mzwaal May 26 '11 at 6:11
 
No I am not using updatepanel. –  Muhammad Akhtar May 26 '11 at 6:12

3 Answers

up vote 1 down vote accepted

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.

share|improve this answer
 
thanks for your answer, but is there any way to do this ? As I have to get value in server side after calling Jquery JSON function. –  Muhammad Akhtar May 26 '11 at 6:22
 
Use a synchronous call to that webservice inside the Button1_Click handler. You can't use JQuery on the server. –  Khanzor May 26 '11 at 6:25
 
Can you please give me idea, how can I do so? –  Muhammad Akhtar May 26 '11 at 6:34
 
new WebClient().DownloadString("Your url here") will give you the result of a web service call. –  Khanzor May 26 '11 at 14:08
up vote 0 down vote

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.

share|improve this answer
up vote 0 down vote

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.

share|improve this answer
 
I know i can do it OnClientClick="JSFunctionName();", but I don't want to that, that's my requirement. –  Muhammad Akhtar May 26 '11 at 6:21
1  
Any particular reason that you don't want to do it this way? –  Matt Hilton May 26 '11 at 6:24
 
as I have to Execute server side code and get time zone from the DB and then pass that time zone to that JS function. –  Muhammad Akhtar May 26 '11 at 6:25

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