How to populate html element using javascript prior to page_load()?

Question

Maybe a chicken/egg problem.

Based on this answer: https://stackoverflow.com/a/27190520/1438215

I want to use javascript to populate the value of an asp.net hidden field (as soon as it's possible), and then access the value of that populated field in the server-side Page_Load event.

Sample:

aspx portion:

<div id="div_BrowserWindowName" style="visibility:hidden;">
    <input type="hidden" name="ctl00$ctl00$BodyContent$MainContent$hf_BrowserWindowName" id="BodyContent_MainContent_hf_BrowserWindowName" />
</div>
<script type="text/javascript">
            function PopBrowserWindowName() {
    if (typeof window.name != undefined) {
        if (window.name == '') {
            var d = new Date();
            window.name = '_myWnd_' + d.getUTCHours() + d.getUTCMinutes() + d.getUTCSeconds() + d.getUTCMilliseconds();
        }
        var eDiv = document.getElementById('div_BrowserWindowName');
        var e = eDiv.getElementsByTagName('input')[0];
        e.value = window.name;
        alert(e.value);
    }
          }

    window.onload = PopBrowserWindowName();
</script>

aspx.cs portion (page_load) event:

if (hf_BrowserWindowName != null)
       {string winID = hf_BrowserWindowName.Value;}

This does works during postbacks, but does not work on the page's initial load.

mason · Accepted Answer · 2015-01-14 18:49:30Z

1

Prior to Page_Load, there is no HTML or JavaScript because the Response has not been sent to the client yet. You need to learn the ASP.NET Page Lifecycle.

You can use server side code to populate the information, or after the page is sent to the client you can have some JavaScript populate the information.

answered Jan 14, 2015 at 18:49

mason

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4 Comments

Douglas Timms Over a year ago

The answer, though not the answer I was hoping for.

mason Over a year ago

@DouglasTimms Why are you trying to get the window name on the server side anyways?

Douglas Timms Over a year ago

Desperate attempt to continue being able to use session variables, yet still have them be unique across multiple tabs within single browser. Trying to implement this solution offered by someone else: stackoverflow.com/a/27190520/1438215

mason Over a year ago

@DouglasTimms Session isn't supposed to be unique, and you're really fighting the architecture if you try to. Concede defeat on that. If you need to save state specific to a certain page, then use ViewState, and pass the data to subsequent pages via query string or posting to different pages.

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