JavaScript usage in Web Part

If you want to use JavaScript in your Web part then you have two options:

1) Refer to some external JavaScript file.

ClientScriptManager cs = Page.ClientScript;
// Include the required javascript file.
if (!cs.IsClientScriptIncludeRegistered("tab_javascript"))
   cs.RegisterClientScriptInclude(this.GetType(), "tab_javascript",          
         "/_layouts/BCLBlast/tab.js");

I placed the JavaScript file at following location:

C:\Program Files\Common Files\Microsoft Shared\web server extensions\12\TEMPLATE\LAYOUTS\BCLBlast

2) Write JavaScript in Web Part file.

// Initialize javascript variables to have list of all tabs and headers
if (!cs.IsClientScriptBlockRegistered("tabs_list"))
{
    string tabVariables = 
                @"<script type=""text/javascript"">" +Environment.NewLine +
                @"var tabs = [{0}] ;" + Environment.NewLine +
                @"var tabheaders = [{1}] ;"+Environment.NewLine+
                @"var _currentTab = null ;" + Environment.NewLine +
                @"</script>";

    string tabPages = "", tabHeaders = "";
    for (int i = 0; i < SearchInformationSources.TotalSearchProviders; i++)
    {
        tabPages += "\"tab" + i.ToString() + "\", ";
        tabHeaders += "\"tabheader" + i.ToString() + "\", ";
    }

    if (tabHeaders.Length > 1)
    {
        tabPages = tabPages.Remove(tabPages.Length - 2, 2);
        tabHeaders = tabHeaders.Remove(tabHeaders.Length - 2, 2);
    }
    
    cs.RegisterClientScriptBlock(GetType(), "tabs_list", 
         String.Format(tabVariables, tabPages, tabHeaders));
}

Whole code snippet is as follows:

protected override void OnPreRender(EventArgs e)
{
    ClientScriptManager cs = Page.ClientScript;
    //Include the required javascript file.
    if (!cs.IsClientScriptIncludeRegistered("tab_javascript"))
        cs.RegisterClientScriptInclude(this.GetType(),
           "tab_javascript", "/_layouts/BCLBlast/tab.js");

    
    // Initialize javascript variables to have list of all tabs and headers
    if (!cs.IsClientScriptBlockRegistered("tabs_list"))
    {
        string tabVariables = 
                   @"<script type=""text/javascript"">" + Environment.NewLine +
                   @"var tabs = [{0}] ;" + Environment.NewLine +
                   @"var tabheaders = [{1}] ;" + Environment.NewLine +
                   @"var _currentTab = null ;" + Environment.NewLine +
                   @"</script>";

        string tabPages = "", tabHeaders = "";
        for (int i = 0; i < SearchInformationSources.TotalSearchProviders; i++)
        {
            tabPages += "\"tab" + i.ToString() + "\", ";
            tabHeaders += "\"tabheader" + i.ToString() + "\", ";
        }

        if (tabHeaders.Length > 1)
        {
            tabPages = tabPages.Remove(tabPages.Length - 2, 2);
            tabHeaders = tabHeaders.Remove(tabHeaders.Length - 2, 2);
        }
        
        cs.RegisterClientScriptBlock(GetType(), "tabs_list", 
             String.Format(tabVariables, tabPages, tabHeaders));
    }
}

Here you to have to implement the OnPreRender method to write the JavaScript code.