How to create a tabpanel (xul) in Javascript - firefox

Question

i dev a Firefox extension and i try to add a tabpanel in a tabbox (xul).
The tabbox:
<tabbox id="tbDashboard" selectedIndex="0" >
<tabs><!-- list of tabs -->
<tab label="Overview"/> <!-- default tab -->
<tab label="test"/>
</tabs>
<tabpanels><!-- list of contents -->
<tabpanel ><!-- default tab's content -->
<box orient="horizontal" flex="1">
<description style="font-size: 24pt;">overview</description>
</box>
</tabpanel>
<tabpanel ><!-- test tab's content -->
<box orient="horizontal" flex="1">
<description style="font-size: 24pt;">test</description>
</box>
</tabpanel>
</tabpanel>
</tabpanels>
</tabbox>
I can add a new tab in JS with:
document.getElementById("tbDashboard")["tabs"].appendItem("popo");
The tab is appears but the tab page is empty, i tried to:
use appendItem with a second parameter => don't work
document.getElementById("tbDashboard")["tabpanels"].appendItem(...) => fail
Someone have an idea to create the tab page (a tabpanel) ??
thx

Answer 1

tabs.appendItem() is merely a convenient helper to create a tab element. It is essentially the same as:
var tabbox = document.getElementById("tbDashboard");
var tab = document.createElement("tab");
tab.textContent = "popo";
tabbox.tabs.appendChild(tab);
You can create and add a tabpanel element in the same way (here with a text box as only contents):
var panel = document.createElement("tabpanel");
panel.appendChild(document.createElement("textbox"));
tabbox.tabpanels.appendChild(panel);
For a tutorial on DOM manipulation see https://developer.mozilla.org/en/XUL_Tutorial/Modifying_a_XUL_Interface.

Answer 2

You'll need to create the panel using the DOM API and then append it to your XUL document, e.g.:
let newPanel = document.createElement("tabpanel");
let panelContent = document.createElement("hbox");
// Add more content here
newPanel.appendChild(panelContent);
document.getElementById("tbDashboard").tabPanels.appendChild(newPanel);