How to share a C# Integer variable with JavaScript

I want to share the currentTab variable which exists on the C# server side with JavaScript. Here is my code:

C#:

public int currentTab = 1;

protected void Page_Load(object sender, EventArgs e)
{
    Page.ClientScript.RegisterStartupScript(Type.GetType("System.String"), "addScript", "showTab(" + currentTab + ");", true);
}

JavaScript:

var currentTab = "<%=currentTab%>";

function showTab(index)
{
    currentTab = index;
    // Show tab at (index)
}

I used this approach to get the current tab again on PostBack. However, currentTab on C# is remains 1 after PostBack. How can I solve this issue?

Answers:

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Method 1

You can write the index from your javascript function, to a hiddenfield, and then read that on postback.

In your code, you check the hiddenfield, if your page is postback.
Like so:

protected void Page_Load(object sender, EventArgs e)
    {
        if (Page.IsPostBack)
        {
            currentTab = Int32.Parse(HiddenTabValue.Value);
        }

    }

Method 2

Have a server side hidden field to hold this piece of information.

You can access the field through javascript and as a server side control the value will be available server side.

Method 3

You need to use some server control to send value back to the server (i.e. asp:HiddenField) or use query string to set the tab index there.

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0