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The context-menu module lets you add items to Firefox's page context menu.
Introduction
The context-menu API provides a simple, declarative way to add items to the
page's context menu. You can add items that perform an action when clicked,
submenus, and menu separators.
Instead of manually adding items when particular contexts occur and then removing them when those contexts go away, you bind items to contexts, and the adding and removing is automatically handled for you. Items are bound to contexts in much the same way that event listeners are bound to events. When the user invokes the context menu, all of the items bound to the current context are automatically added to the menu. If no items are bound, none are added. Likewise, any items that were previously in the menu but are not bound to the current context are automatically removed from the menu. You never need to manually remove your items from the menu unless you want them to never appear again.
For example, if your add-on needs to add a context menu item whenever the user visits a certain page, don't create the item when that page loads, and don't remove it when the page unloads. Rather, create your item only once and supply a context that matches the target URL.
Context menu items are displayed in the order created or in the case of sub
menus the order added to the sub menu. Menu items for each add-on will be
grouped together automatically. If the total number of menu items in the main
context menu from all add-ons exceeds a certain number (normally 10 but
configurable with the extensions.addon-sdk.context-menu.overflowThreshold
preference) all of the menu items will instead appear in an overflow menu to
avoid making the context menu too large.
Specifying Contexts
As its name implies, the context menu should be reserved for the occurrence of specific contexts. Contexts can be related to page content or the page itself, but they should never be external to the page.
For example, a good use of the menu would be to show an "Edit Image" item when the user right-clicks an image in the page. A bad use would be to show a submenu that listed all the user's tabs, since tabs aren't related to the page or the node the user clicked to open the menu.
The Page Context
First of all, you may not need to specify a context at all. When a top-level item does not specify a context, the page context applies. An item that is in a submenu is visible unless you specify a context.
The page context occurs when the user invokes the context menu on a non-interactive portion of the page. Try right-clicking a blank spot in this page, or on text. Make sure that no text is selected. The menu that appears should contain the items "Back", "Forward", "Reload", "Stop", and so on. This is the page context.
The page context is appropriate when your item acts on the page as a whole. It does not occur when the user invokes the context menu on a link, image, or other non-text node, or while a selection exists.
Declarative Contexts
You can specify some simple, declarative contexts when you create a menu item by
setting the context property of the options object passed to its constructor,
like this:
var cm = require("sdk/context-menu");
cm.Item({
label: "My Menu Item",
context: cm.URLContext("*.mozilla.org")
});
These contexts may be specified by calling the following constructors. Each is
exported by the context-menu module.
| Constructor | Description |
|---|---|
PageContext()
|
The page context. |
SelectionContext()
|
This context occurs when the menu is invoked on a page in which the user has made a selection. |
SelectorContext(selector)
|
This context occurs when the menu is invoked on a node that either matches
selector, a CSS selector, or has an ancestor that matches.
selector may include multiple selectors separated by commas,
e.g., "a[href], img".
|
URLContext(matchPattern)
|
This context occurs when the menu is invoked on pages with particular
URLs. matchPattern is a match pattern string or an array of
match pattern strings. When matchPattern is an array, the
context occurs when the menu is invoked on a page whose URL matches any of
the patterns. These are the same match pattern strings that you use with
the page-mod
include property.
Read more about patterns.
|
| array | An array of any of the other types. This context occurs when all contexts in the array occur. |
Menu items also have a context property that can be used to add and remove
declarative contexts after construction. For example:
var context = require("sdk/context-menu").SelectorContext("img");
myMenuItem.context.add(context);
myMenuItem.context.remove(context);
When a menu item is bound to more than one context, it appears in the menu when all of those contexts occur.
In Content Scripts
The declarative contexts are handy but not very powerful. For instance, you might want your menu item to appear for any page that has at least one image, but declarative contexts won't help you there.
When you need more control over the context in which your menu items are
shown, you can use content scripts. Like other APIs in the SDK, the
context-menu API uses
content scripts to let your
add-on interact with pages in the browser. Each menu item you create in the
top-level context menu can have a content script.
A special event named "context" is emitted in your content scripts whenever
the context menu is about to be shown. If you register a listener function for
this event and it returns true, the menu item associated with the listener's
content script is shown in the menu.
For example, this item appears whenever the context menu is invoked on a page that contains at least one image:
require("sdk/context-menu").Item({
label: "This Page Has Images",
contentScript: 'self.on("context", function (node) {' +
' return !!document.querySelector("img");' +
'});'
});
Note that the listener function has a parameter called node. This is the node
in the page that the user context-clicked to invoke the menu. You can use it to
determine whether your item should be shown.
You can both specify declarative contexts and listen for contexts in a content script. In that case, the declarative contexts are evaluated first, and your item is shown only when all declarative contexts are current and your context listener returns true.
If any declarative contexts are not current, then your context listener
is never called. This example takes advantage of that fact. The listener
can be assured that node will always be an image:
var cm = require("sdk/context-menu");
cm.Item({
label: "A Mozilla Image",
context: cm.SelectorContext("img"),
contentScript: 'self.on("context", function (node) {' +
' return /mozilla/.test(node.src);' +
'});'
});
However, if you do combine SelectorContext and the "context" event,
be aware that the node argument passed to the "context" event will
not always match the type specified in SelectorContext.
SelectorContext will match if the menu is invoked on the node specified
or any descendant of that node, but the "context" event handler is
passed the actual node on which the menu was invoked. The example above
works because <IMG> elements can't contain other elements, but in the
example below, node.nodeName is not guaranteed to be "P" - for example,
it won't be "P" if the user context-clicked a link inside a paragraph:
var cm = require("sdk/context-menu");
cm.Item({
label: "A Paragraph",
context: cm.SelectorContext("p"),
contentScript: 'self.on("context", function (node) {' +
' console.log(node.nodeName);' +
' return true;' +
'});'
});
The content script is executed for every page that a context menu is shown for. It will be executed the first time it is needed (i.e. when the context menu is first shown and all of the declarative contexts for your item are current) and then remains active until you destroy your context menu item or the page is unloaded.
Handling Menu Item Clicks
In addition to using content scripts to listen for the "context" event as
described above, you can use content scripts to handle item clicks. When the
user clicks your menu item, an event named "click" is emitted in the item's
content script.
Therefore, to handle an item click, listen for the "click" event in that
item's content script like so:
require("sdk/context-menu").Item({
label: "My Item",
contentScript: 'self.on("click", function (node, data) {' +
' console.log("Item clicked!");' +
'});'
});
Note that the listener function has parameters called node and data.
The "node" Argument
node is the node that the user context-clicked to invoke the menu.
- If you did not use
SelectorContextto decide whether to show the menu item, then this is the actual node clicked. - If you did use
SelectorContext, then this is the node that matched your selector.
For example, suppose your add-on looks like this:
var script = "self.on('click', function (node, data) {" +
" console.log('clicked: ' + node.nodeName);" +
"});";
var cm = require("sdk/context-menu");
cm.Item({
label: "body context",
context: cm.SelectorContext("body"),
contentScript: script
});
This add-on creates a context-menu item that uses SelectorContext to display
the item whenever the context menu is activated on any descendant of the
<BODY> element. When clicked, the item just logs the
nodeName
property for the node passed to the click handler.
If you run this add-on you'll see that it always logs "BODY", even if you click on a paragraph element inside the page:
info: contextmenu-example: clicked: BODY
By contrast, this add-on uses the PageContext:
var script = "self.on('click', function (node, data) {" +
" console.log('clicked: ' + node.nodeName);" +
"});";
var cm = require("sdk/context-menu");
cm.Item({
label: "body context",
context: cm.PageContext(),
contentScript: script
});
It will log the name of the actual node clicked:
info: contextmenu-example: clicked: P
The "data" Argument
data is the data property of the menu item
that was clicked. Note that when you have a hierarchy of menu items the click
event will be sent to the content script of the item clicked and all ancestors
so be sure to verify that the data value passed matches the item you expect.
You can use this to simplify click handling by providing just a single click
listener on a Menu that reacts to clicks for any child items.:
var cm = require("sdk/context-menu");
cm.Menu({
label: "My Menu",
contentScript: 'self.on("click", function (node, data) {' +
' console.log("You clicked " + data);' +
'});',
items: [
cm.Item({ label: "Item 1", data: "item1" }),
cm.Item({ label: "Item 2", data: "item2" }),
cm.Item({ label: "Item 3", data: "item3" })
]
});
Communicating With the Add-on
Often you will need to collect some kind of information in the click listener
and perform an action unrelated to content. To communicate to the menu item
associated with the content script, the content script can call the
postMessage function attached to the global self object, passing it some
JSON-able data. The menu item's "message" event listener will be called with
that data.
var cm = require("sdk/context-menu");
cm.Item({
label: "Edit Image",
context: cm.SelectorContext("img"),
contentScript: 'self.on("click", function (node, data) {' +
' self.postMessage(node.src);' +
'});',
onMessage: function (imgSrc) {
openImageEditor(imgSrc);
}
});
Updating a Menu Item's Label
Each menu item must be created with a label, but you can change its label later using a couple of methods.
The simplest method is to set the menu item's label property. This example
updates the item's label based on the number of times it's been clicked:
var numClicks = 0;
var myItem = require("sdk/context-menu").Item({
label: "Click Me: " + numClicks,
contentScript: 'self.on("click", self.postMessage);',
onMessage: function () {
numClicks++;
this.label = "Click Me: " + numClicks;
// Setting myItem.label is equivalent.
}
});
Sometimes you might want to update the label based on the context. For
instance, if your item performs a search with the user's selected text, it would
be nice to display the text in the item to provide feedback to the user. In
these cases you can use the second method. Recall that your content scripts can
listen for the "context" event and if your listeners return true, the items
associated with the content scripts are shown in the menu. In addition to
returning true, your "context" listeners can also return strings. When a
"context" listener returns a string, it becomes the item's new label.
This item implements the aforementioned search example:
var cm = require("sdk/context-menu");
cm.Item({
label: "Search Google",
context: cm.SelectionContext(),
contentScript: 'self.on("context", function () {' +
' var text = window.getSelection().toString();' +
' if (text.length > 20)' +
' text = text.substr(0, 20) + "...";' +
' return "Search Google for " + text;' +
'});'
});
The "context" listener gets the window's current selection, truncating it if
it's too long, and includes it in the returned string. When the item is shown,
its label will be "Search Google for text", where text is the truncated
selection.
More Examples
For conciseness, these examples create their content scripts as strings and use
the contentScript property. In your own add-on, you will probably want to
create your content scripts in separate files and pass their URLs using the
contentScriptFile property. See
Working with Content Scripts
for more information.
Unless your content script is extremely simple and consists only of a
static string, don't use contentScript: if you do, you may
have problems getting your add-on approved on AMO.
Instead, keep the script in a separate file and load it using
contentScriptFile. This makes your code easier to maintain,
secure, debug and review.
Show an "Edit Page Source" item when the user right-clicks a non-interactive part of the page:
require("sdk/context-menu").Item({
label: "Edit Page Source",
contentScript: 'self.on("click", function (node, data) {' +
' self.postMessage(document.URL);' +
'});',
onMessage: function (pageURL) {
editSource(pageURL);
}
});
Show an "Edit Image" item when the menu is invoked on an image:
var cm = require("sdk/context-menu");
cm.Item({
label: "Edit Image",
context: cm.SelectorContext("img"),
contentScript: 'self.on("click", function (node, data) {' +
' self.postMessage(node.src);' +
'});',
onMessage: function (imgSrc) {
openImageEditor(imgSrc);
}
});
Show an "Edit Mozilla Image" item when the menu is invoked on an image in a mozilla.org or mozilla.com page:
var cm = require("sdk/context-menu");
cm.Item({
label: "Edit Mozilla Image",
context: [
cm.URLContext(["*.mozilla.org", "*.mozilla.com"]),
cm.SelectorContext("img")
],
contentScript: 'self.on("click", function (node, data) {' +
' self.postMessage(node.src);' +
'});',
onMessage: function (imgSrc) {
openImageEditor(imgSrc);
}
});
Show an "Edit Page Images" item when the page contains at least one image:
var cm = require("sdk/context-menu");
cm.Item({
label: "Edit Page Images",
// This ensures the item only appears during the page context.
context: cm.PageContext(),
contentScript: 'self.on("context", function (node) {' +
' var pageHasImgs = !!document.querySelector("img");' +
' return pageHasImgs;' +
'});' +
'self.on("click", function (node, data) {' +
' var imgs = document.querySelectorAll("img");' +
' var imgSrcs = [];' +
' for (var i = 0 ; i < imgs.length; i++)' +
' imgSrcs.push(imgs[i].src);' +
' self.postMessage(imgSrcs);' +
'});',
onMessage: function (imgSrcs) {
openImageEditor(imgSrcs);
}
});
Show a "Search With" menu when the user right-clicks an anchor that searches Google or Wikipedia with the text contained in the anchor:
var cm = require("sdk/context-menu");
var googleItem = cm.Item({
label: "Google",
data: "http://www.google.com/search?q="
});
var wikipediaItem = cm.Item({
label: "Wikipedia",
data: "http://en.wikipedia.org/wiki/Special:Search?search="
});
var searchMenu = cm.Menu({
label: "Search With",
context: cm.SelectorContext("a[href]"),
contentScript: 'self.on("click", function (node, data) {' +
' var searchURL = data + node.textContent;' +
' window.location.href = searchURL;' +
'});',
items: [googleItem, wikipediaItem]
});
@argument {value} Listeners are passed a single argument which is the message posted from the content script. The message can be any JSON-serializable value.
@class A labeled menu item that expands into a submenu. @constructor Creates a labeled menu item that expands into a submenu. @param options {object} An object with the following keys: @prop label {string} The item's label. It must either be a string or an object that implements `toString()`. @prop items {array} An array of menu items that the menu will contain. Each must be an `Item`, `Menu`, or `Separator`. @prop [image] {string} The menu's icon, a string URL. The URL can be remote, a reference to an image in the add-on's `data` directory, or a data URI. @prop [context] {value} If the menu is contained in the top-level context menu, this declaratively specifies the context under which the menu will appear; see Specifying Contexts above. @prop [contentScript] {string,array} If the menu is contained in the top-level context menu, this is the content script or an array of content scripts that the menu can use to interact with the page. @prop [contentScriptFile] {string,array} If the menu is contained in the top-level context menu, this is the local file URL of the content script or an array of such URLs that the menu can use to interact with the page. @prop [onMessage] {function} If the menu is contained in the top-level context menu, this function will be called when the content script calls `self.postMessage`. It will be passed the data that was passed to `postMessage`. @property {string} The menu's label. You can set this after creating the menu to update its label later. @property {array} An array containing the items in the menu. The array is read-only, meaning that modifications to it will not affect the menu. However, setting this property to a new array will replace all the items currently in the menu with the items in the new array. @property {string} The menu's icon, a string URL. The URL can be remote, a reference to an image in the add-on's `data` directory, or a data URI. You can set this after creating the menu to update its image later. To remove the menu's image, set it to `null`. @property {list} A list of declarative contexts for which the menu will appear in the context menu. Contexts can be added by calling `context.add()` and removed by called `context.remove()`. @property {Menu} The menu's parent `Menu`, or `null` if the menu is contained in the top-level context menu. This property is read-only. To add the menu to a new menu, call that menu's `addItem()` method. @property {string,array} The content script or the array of content scripts associated with the menu during creation. @property {string,array} The URL of a content script or the array of such URLs associated with the menu during creation. @method Appends a menu item to the end of the menu. If the item is already contained in another menu or in the top-level context menu, it's automatically removed first. If the item is already contained in this menu it will just be moved to the end of the menu. @param item {Item,Menu,Separator} The `Item`, `Menu`, or `Separator` to add to the menu. @method Removes the given menu item from the menu. If the menu does not contain the item, this method does nothing. @param item {Item,Menu,Separator} The menu item to remove from the menu. @method Permanently removes the menu from its parent menu and frees its resources. The menu must not be used afterward. If you need to remove the menu from its parent menu but use it afterward, call `removeItem()` on the parent menu instead. @event If you listen to this event you can receive message events from content scripts associated with this menu item. When a content script posts a message using `self.postMessage()`, the message is delivered to the add-on code in the menu item's `message` event.@argument {value} Listeners are passed a single argument which is the message posted from the content script. The message can be any JSON-serializable value.
@class A menu separator. Separators can be contained only in `Menu`s, not in the top-level context menu. @constructor Creates a menu separator. @property {Menu} The separator's parent `Menu`. This property is read-only. To add the separator to a new menu, call that menu's `addItem()` method. @method Permanently removes the separator from its parent menu and frees its resources. The separator must not be used afterward. If you need to remove the separator from its parent menu but use it afterward, call `removeItem()` on the parent menu instead. @class @constructor Creates a page context. See Specifying Contexts above. @class @constructor Creates a context that occurs when a page contains a selection. See Specifying Contexts above. @class @constructor Creates a context that matches a given CSS selector. See Specifying Contexts above. @param selector {string} A CSS selector. @class @constructor Creates a context that matches pages with particular URLs. See Specifying Contexts above. @param matchPattern {string,array} A [match pattern](modules/sdk/page-mod/match-pattern.html) string, regexp or an array of match pattern strings or regexps.