devtools.panels.ExtensionSidebarPane.onShown

browser.devtools.panels.onShown.addListener(listener)
browser.devtools.panels.onShown.removeListener(listener)
browser.devtools.panels.onShown.hasListener(listener)

Events have three functions:

addListener(listener)

Adds a listener to this event.

removeListener(listener)

Stop listening to this event. The listener argument is the listener to remove.

hasListener(listener)

Check whether listener is registered for this event. Returns true if it is listening, false otherwise.

listener

The function called when this event occurs. The function is passed this argument:

window

object. The window object of the sidebar page, if a page was set with setPage().

Create a sidebar pane, and log show and hide events.

function onCreated(sidebarPane) {
  sidebarPane.onShown.addListener(() => {
    console.log("Shown");
  });

  sidebarPane.onHidden.addListener(() => {
    console.log("Hidden");
  });
}

browser.devtools.panels.elements.createSidebarPane("My pane").then(onCreated);