menus.onShown 编辑

Fired when the browser has shown a menu.

An extension can use this event to update its menu items using information that's only available once the menu is shown. Typically an extension will figure out the update in its onShown handler and then call menus.refresh() to update the menu itself.

The handler can add, remove, or update menu items.

For example, the menu-labelled-open example extension adds a menu item that's shown when the user clicks a link, and that, when clicked, just opens the link. It uses onShown and refresh() to annotate the menu item with the hostname for the link, so the user can easily see where they will go before they click.

Note that an extension should not take too much time before calling refresh(), or the update will be noticeable to the user.

The handler is passed some information about the menu and its contents, and some information from the page (such as the link and/or selection text). To get access to the information from the page, your extension must have the host permission for it.

If the onShown handler calls any asynchronous APIs, then it's possible that the menu has been closed again before the handler resumes execution. Because of this, if a handler calls any asynchronous APIs, it should check that the menu is still being displayed before it updates the menu. For example:

var lastMenuInstanceId = 0;
var nextMenuInstanceId = 1;

browser.menus.onShown.addListener(async function(info, tab) {
  var menuInstanceId = nextMenuInstanceId++;
  lastMenuInstanceId = menuInstanceId;

  // Call an async function
  await .... ;

  // After completing the async operation, check whether the menu is still shown.
  if (menuInstanceId !== lastMenuInstanceId) {
    return; // Menu was closed and shown again.
  }
  // Now use menus.create/update + menus.refresh.
});

browser.menus.onHidden.addListener(function() {
  lastMenuInstanceId = 0;
});

Note that it is possible to call menus API functions synchronously, and in this case you don't have to perform this check:

browser.menus.onShown.addListener(async function(info, tab) {
  browser.menus.update(menuId, ...);
   // Note: Not waiting for returned promise.
  browser.menus.refresh();
});

However, if you call these APIs asynchronously, then you do have to perform the check:

browser.menus.onShown.addListener(async function(info, tab) {
  var menuInstanceId = nextMenuInstanceId++;
  lastMenuInstanceId = menuInstanceId;

  await browser.menus.update(menuId, ...);
  // must now perform the check
  if (menuInstanceId !== lastMenuInstanceId) {
    return;
  }
  browser.menus.refresh();
});

Firefox makes this event available via the contextMenus namespace as well as the menus namespace.

Syntax

browser.menus.onShown.addListener(listener)
browser.menus.onShown.removeListener(listener)
browser.menus.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.

addListener syntax

Parameters

callback

Function that will be called when this event occurs. The function will be passed the following arguments:

info

Object. This is just like the menus.OnClickData object, except it contains two extra properties:

• contexts: an array of all the contexts that are applicable to this menu.
• menuIds: an array of IDs of all menu items belonging to this extension that are being shown in this menu.

Compared with menus.OnClickData, the info object also omits the menuItemId and modifiers properties, because of course these are not available until a menu item has been selected.

The contexts, menuIds, frameId, and editable properties are always provided. All the other properties in info are only provided if the extension has the host permission for the page.

tab

tabs.Tab. The details of the tab where the click took place. If the click did not take place in or on a tab, this parameter will be missing.

Browser compatibility

BCD tables only load in the browser

The compatibility table in this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.

Examples

This example listens for the context menu to be shown over a link, then updates the openLabelledId menu item with the link's hostname:

function updateMenuItem(linkHostname) {
  browser.menus.update(openLabelledId, {
    title: `Open (${linkHostname})`
  });
  browser.menus.refresh();
}

browser.menus.onShown.addListener(info => {
  if (!info.linkUrl) {
    return;
  }
  let linkElement = document.createElement("a");
  linkElement.href = info.linkUrl;
  updateMenuItem(linkElement.hostname);
});

Example extensions

• menu-labelled-open