mozilla-central/toolkit/content/widgets/panel-list/README.stories.md

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# Panel Menu
The `panel-list` and `panel-item` components work together to create a menu for
in-content contexts. The basic structure is a `panel-list` with `panel-item`
children and optional `hr` elements as separators. The `panel-list` will anchor
itself to the target of the initiating event when opened with
`panelList.toggle(event)`.
Note: XUL is currently required to
support accesskey underlining (although using `moz-label` could change that).
Shortcuts are not displayed automatically in the `panel-item`.
```html story
<panel-list stay-open open>
<panel-item action="new" accesskey="N">New</panel-item>
<panel-item accesskey="O">Open</panel-item>
<hr />
<panel-item action="save" accesskey="S">Save</panel-item>
<hr />
<panel-item accesskey="Q">Quit</panel-item>
</panel-list>
```
## Status
Current status is listed as in-development since this is only intended for use
within in-content contexts. XUL is still required for accesskey underlining, but
could be migrated to use the `moz-label` component. This is a useful but
historical element that could likely use some attention at the API level and to
be brought up to our design systems standards.
## When to use
* When there are multiple options for something that would take too
much space with individual buttons.
* When the actions are not frequently needed.
* When you are within an in-content context.
## When not to use
* When there is only one action.
* When the actions are frequently needed.
* In the browser chrome, you probably want to use
or
instead.
## Basic usage
The source for `panel-list` can be found under
You can find an examples of `panel-list` in use in the Firefox codebase in both
and the
`panel-list` will automatically be imported in chrome documents, both through
markup and through JS with `document.createElement("panel-list")` or by cloning
a template.
```html
<!-- This will import `panel-list` if needed in most cases. -->
<panel-list></panel-list>
```
In non-chrome documents it can be imported into `.html`/`.xhtml` files:
```html
```
And used as follows:
```html
<panel-list>
<panel-item accesskey="N">New</panel-item>
<panel-item accesskey="O">Open</panel-item>
<hr />
<panel-item accesskey="S">Save</panel-item>
<hr />
<panel-item accesskey="Q">Quit</panel-item>
</panel-list>
```
The `toggle` method takes the event you received on your anchor button and opens
the menu attached to that element.
```js
anchorButton.addEventListener("mousedown", e => panelList.toggle(e));
```
Accesskeys are activated with the bare accesskey letter when the menu is opened.
So for this example after opening the menu pressing `s` will fire a click event
on the Save `panel-item`.
Note: XUL is currently required for accesskey underlining, but can be [replaced
### Fluent usage
The `panel-item` expects to have text content set by fluent.
```html
<panel-list>
<panel-item data-l10n-id="menu-new"></panel-item>
<panel-item data-l10n-id="menu-save"></panel-item>
</panel-list>
```
In which case your Fluent messages will look something like this:
```
menu-new = New
.accesskey = N
menu-save = Save
.accesskey = S
```
## Advanced usage
### Showing the menu
By default the menu will be hidden. It is shown when the `open` attribute is
set, but that won't position the menu by default.
To trigger the auto-positioning of the menu, it should be opened or closed using
the `toggle(event)` method.
```js
function onMenuButton(event) {
document.querySelector("panel-list").toggle(event);
}
```
The `toggle(event)` method will use `event.target` as the anchor for the menu.
To achieve the expected behaviour, the menu should open on `mousedown` for mouse
events, and `click` for keyboard events. This can be accomplished by checking
the `event.inputSource` property in chrome contexts or `event.detail` in
non-chrome contexts (`event.detail` will be the click count which is `0` when a
click is from the keyboard).
```js
function openMenu(event) {
if (
event.type == "mousedown" ||
event.inputSource == MouseEvent.MOZ_SOURCE_KEYBOARD ||
!event.detail
) {
document.querySelector("panel-list").toggle(event);
}
}
let menuButton = document.getElementById("open-menu-button");
menuButton.addEventListener("mousedown", openMenu);
menuButton.addEventListener("click", openMenu);
```
### Icons
Icons can be added to the `panel-item`s by setting a `background-image` on
`panel-item::part(button)`.
```css
panel-item[action="new"]::part(button) {
background-image: url("./new.svg");
}
panel-item[action="save"]::part(button) {
background-image: url("./save.svg");
}
```
### Badging
Icons may be badged by setting the `badged` attribute. This adds a dot next to
the icon.
```html
<panel-list>
<panel-item action="new">New</panel-item>
<panel-item action="save" badged>Save</panel-item>
</panel-list>
```
```html story
<panel-list stay-open open>
<panel-item action="new">New</panel-item>
<panel-item action="save" badged>Save</panel-item>
</panel-list>
```
### Matching anchor width
When using the `panel-list` like a `select` dropdown, it's nice to have it match
the size of the anchor button. You can see this in practice in the
[Wide variant](?path=/story/ui-widgets-panel-list--wide) and the
`migration-wizard`. Setting the `min-width-from-anchor` attribute will cause the
menu to match its anchor's width when it is opened.
```html
<button class="current-selection">Apples</button>
<panel-list min-width-from-anchor>
<panel-item>Apples</panel-list>
<panel-item>Bananas</panel-list>
</panel-list>
```
### Usage in a XUL `panel`
The "new" (as of early 2023) migration wizard uses the `panel-list` inside of a
XUL `panel` element to let its contents escape its container dialog by creating
an OS-level window. This can be useful if the menu could be larger than its
container, however in chrome contexts you are likely better off using
`menupopup`.
By placing a `panel-list` inside of a XUL `panel` it will automatically defer
its positioning responsibilities to the XUL `panel` and it will then be able to
grow larger than its containing window if needed.
```html
<!-- Assuming we're in a XUL document. -->
<panel>
<html:panel-list>
<html:panel-item>Apples</html:panel-item>
<html:panel-item>Apples</html:panel-item>
<html:panel-item>Apples</html:panel-item>
</html:panel-list>
</panel>
```
### Submenus
`panel-list` supports nested submenus. Submenus can be created by nesting a second `panel-list` in a `panel-item`'s `submenu` slot and specifying a `submenu` attribute on that `panel-item` that points to the nested list's ID. For example:
```html
<panel-list>
<panel-item>No submenu</panel-item>
<panel-item>No submenu</panel-item>
<panel-item submenu="example-submenu">
Has a submenu
<panel-list slot="submenu" id="example-submenu">
<panel-item>I'm a submenu item!</panel-item>
<panel-item>I'm also a submenu item!</panel-item>
</panel-list>
</panel-item>
</panel-list>
```
As of February 2024 submenus are only in use in Firefox View and support for nesting beyond one submenu may be limited.