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   - License, v. 2.0. If a copy of the MPL was not distributed with this
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<!-- contributed by Nickolay Ponomarev [asqueella@gmail.com] -->
<!-- contributed by Myk Melez [myk@mozilla.org] -->
<!-- contributed by Irakli Gozalishvil [gozala@mozilla.com] -->

The `page-mod` module enables you to run scripts in the context of
specific web pages. To use it, you specify:

* one or more scripts to attach. The SDK calls these scripts "content scripts".
* a pattern that a page's URL must match, in order for the script(s)
to be attached to that page.

For example, the following add-on displays an alert whenever the user
visits any page hosted at "mozilla.org":

    var pageMod = require("page-mod");

    pageMod.PageMod({
      include: "*.mozilla.org",
      contentScript: 'window.alert("Page matches ruleset");'
    });

You can modify the document in your script:

    var pageMod = require("page-mod");

    pageMod.PageMod({
      include: "*.mozilla.org",
      contentScript: 'document.body.innerHTML = ' +
                     ' "<h1>Page mpackages_diratches ruleset</h1>";'
    });

You can supply the content script(s) in one of two ways:

* as a string literal, or an array of string literals, assigned to the `contentScript` option, as above
* as separate files supplied in your add-on's "data" directory.
In this case files are specified by a URL typically constructed using the
`url()` method of the
[`self` module's `data` object](modules/sdk/self.html#data):

<!-- -->

    var data = require("self").data;
    var pageMod = require("page-mod");
    pageMod.PageMod({
      include: "*.mozilla.org",
      contentScriptFile: data.url("my-script.js")
    });

<!-- -->

    var data = require("self").data;
    var pageMod = require("page-mod");

    pageMod.PageMod({
      include: "*.mozilla.org",
      contentScriptFile: [self.data.url("jquery-1.7.min.js"),
                          self.data.url("my-script.js")]
    });

<div class="warning">
<p>Unless your content script is extremely simple and consists only of a
static string, don't use <code>contentScript</code>: if you do, you may
have problems getting your add-on approved on AMO.</p>
<p>Instead, keep the script in a separate file and load it using
<code>contentScriptFile</code>. This makes your code easier to maintain,
secure, debug and review.</p>
</div>

A page-mod only attaches scripts to documents loaded in tabs. It will not
attach scripts to add-on panels, page-workers, widgets, or Firefox hidden
windows.

To stop a page-mod from making any more modifications, call its `destroy()`
method.

The `PageMod` constructor takes a number of other options to control its
behavior, all documented in detail in the
[API Reference](modules/sdk/page-mod.html#API Reference) section below:

* `contentStyle` or `contentStyleFile` list stylesheets to attach.
* `contentScriptOptions` defines read-only values accessible to content
scripts.
* `attachTo` controls whether to attach scripts to tabs
that were already open when the page-mod was created, and whether to attach
scripts to iframes as well as the topmost document.
* `contentScriptWhen` controls the point during document load at which content
scripts are attached.

For all the details on content scripts, see the
[guide to content scripts](dev-guide/guides/content-scripts/index.html).

## Communicating With Content Scripts ##

Your add-on's "main.js" can't directly access the state of content scripts
you load, but you can communicate between your add-on and its content scripts
by exchanging messages.

To do this, you'll need to listen to the page-mod's `attach` event.
This event is triggered every time the page-mod's content script is attached
to a document. The listener is passed a
[`worker`](modules/sdk/content/worker.html) object that your add-on
can use to send and receive messages.

For example, the following add-on retrieves the HTML content of specific
tags from documents that match the pattern. The main add-on code sends the
desired tag to the content script, and the content script replies by sending
the HTML content of all the elements with that tag.

/lib/main.js:

    var tag = "p";
    var data = require("self").data;
    var pageMod = require("page-mod");

    pageMod.PageMod({
      include: "*.mozilla.org",
      contentScriptFile: data.url("element-getter.js"),
      onAttach: function(worker) {
        worker.port.emit("getElements", tag);
        worker.port.on("gotElement", function(elementContent) {
          console.log(elementContent);
        });
      }
    });

/data/element-getter.js:

    self.port.on("getElements", function(tag) {
      var elements = document.getElementsByTagName(tag);
      for (var i = 0; i < elements.length; i++) {
        self.port.emit("gotElement", elements[i].innerHTML);
      }
    });

When the user loads a document hosted at "mozilla.org":

<img class="image-right" alt="page-mod messaging diagram" src="static-files/media/page-mod-messaging.png"/>

* The content script "element-getter.js" is attached to the document
and runs. It adds a listener to the `getElements` message.
* The `attach` event is sent to the "main.js" code. Its event handler sends
the `getElements` message to the content script, and then adds a listener
to the `gotElement` message.
* The content script receives the `getElements` message, retrieves all
elements of that type, and for each element sends a `gotElement` message
containing the element's `innerHTML`.
* The "main.js" code receives each `gotElement` message and logs the
contents.

If multiple documents that match the page-mod's `include` pattern are loaded,
then each document is loaded into its own execution context with its own copy
of the content scripts. In this case the listener assigned to `onAttach`
is called once for each loaded document, and the add-on code will have a
separate worker for each document.

To learn much more about communicating with content scripts, see the
[guide to content scripts](dev-guide/guides/content-scripts/index.html) and in
particular the chapter on
[communicating using `port`](dev-guide/guides/content-scripts/using-port.html).

## Mapping Workers to Tabs ##

The `worker` has a `tab` property which returns the tab associated with
this worker. You can use this to access
the [`tabs API`](modules/sdk/tabs.html) for the tab associated
with a specific document:

    var pageMod = require("page-mod");
    var tabs = require("tabs");

    pageMod.PageMod({
      include: ["*"],
      onAttach: function onAttach(worker) {
        console.log(worker.tab.title);
      }
    });

## Destroying Workers ##

Workers generate a `detach` event when their associated document is closed:
that is, when the tab is closed or the tab's location changes. If
you are maintaining a list of workers belonging to a page-mod, you can use
this event to remove workers that are no longer valid.

For example, if you maintain a list of workers attached to a page-mod:

    var workers = [];

    var pageMod = require("page-mod").PageMod({
      include: ['*'],
      contentScriptWhen: 'ready',
      contentScriptFile: data.url('pagemod.js'),
      onAttach: function(worker) {
        workers.push(worker);
      }
    });

You can remove workers when they are no longer valid by listening to `detach`:

    var workers = [];

    function detachWorker(worker, workerArray) {
      var index = workerArray.indexOf(worker);
      if(index != -1) {
        workerArray.splice(index, 1);
      }
    }

    var pageMod = require("page-mod").PageMod({
      include: ['*'],
      contentScriptWhen: 'ready',
      contentScriptFile: data.url('pagemod.js'),
      onAttach: function(worker) {
        workers.push(worker);
        worker.on('detach', function () {
          detachWorker(this, workers);
        });
      }
    });


## Attaching Content Scripts to Tabs ##

We've seen that the page-mod API attaches content scripts to documents based
on their URL. Sometimes, though, we don't care about the URL: we just want
to execute a script on demand in the context of a particular tab.

For example, we might want to run a script in the context of the currently
active tab when the user clicks a widget: to block certain content, to
change the font style, or to display the document's DOM structure.

Using the `attach` method of the [`tab`](modules/sdk/tabs.html)
object, you can attach a set of content scripts to a particular tab. The
scripts are executed immediately.

The following add-on creates a widget which, when clicked, highlights all the
`div` elements in the document loaded into the active tab:

    var widgets = require("widget");
    var tabs = require("tabs");

    var widget = widgets.Widget({
      id: "div-show",
      label: "Show divs",
      contentURL: "http://www.mozilla.org/favicon.ico",
      onClick: function() {
        tabs.activeTab.attach({
          contentScript:
            'var divs = document.getElementsByTagName("div");' +
            'for (var i = 0; i < divs.length; ++i) {' +
              'divs[i].setAttribute("style", "border: solid red 1px;");' +
            '}'
        });
      }
    });

<api name="PageMod">
@class
A page-mod object. Once created a page-mod will execute the supplied content
scripts, and load any supplied stylesheets, in the context of any documents
matching the pattern specified by the `include` property.

<api name="PageMod">
@constructor
Creates a page-mod.
@param options {object}
  Options for the page-mod. All these options are optional except for `include`
  (although if you don't supply any scripts or stylesheets, your page-mod
  won't be very useful).
  @prop include {string,array}
    A match pattern string or an array of match pattern strings.  These define
    the documents to which the page-mod applies. At least one match pattern
    must be supplied.

    You can specify a URL exactly:

        var pageMod = require("page-mod");
        pageMod.PageMod({
          include: "http://www.iana.org/domains/example/",
          contentScript: 'window.alert("Page matches ruleset");'
        });

    You can specify a number of wildcard forms, for example:

        var pageMod = require("page-mod");
        pageMod.PageMod({
          include: "*.mozilla.org",
          contentScript: 'window.alert("Page matches ruleset");'
        });

    You can specify a set of URLs using a
    [regular expression](modules/sdk/page-mod/match-pattern.html#Regular Expressions).
    The pattern must match the entire URL, not just a subset, and has
    `global`, `ignoreCase`, and `multiline` disabled.

        var pageMod = require("page-mod");
        pageMod.PageMod({
          include: /.*developer.*/,
          contentScript: 'window.alert("Page matches ruleset");'
        });

  To specify multiple patterns, pass an array of match patterns:

      var pageMod = require("page-mod");
      pageMod.PageMod({
        include: ["*.developer.mozilla.org", "*.addons.mozilla.org"],
        contentScript: 'window.alert("Page matches ruleset");'
      });

    See the [match-pattern](modules/sdk/page-mod/match-pattern.html) module for
    a detailed description of match pattern syntax.

  @prop [contentScriptFile] {string,array}
    This option specifies one or more content scripts to attach to targeted
    documents.

    Each script is supplied as a separate file under your add-on's "data"
    directory, and is specified by a URL typically constructed using the
    `url()` method of the
    [`self` module's `data` object](modules/sdk/self.html#data).

        var data = require("self").data;
        var pageMod = require("page-mod");
        pageMod.PageMod({
          include: "*",
          contentScriptFile: data.url("my-script.js")
        });

    To attach multiple scripts, pass an array of URLs.

        var data = require("self").data;
        var pageMod = require("page-mod");

        pageMod.PageMod({
          include: "*",
          contentScriptFile: [self.data.url("jquery-1.7.min.js"),
                              self.data.url("my-script.js")]
        });

    Content scripts specified using this option are loaded before those
    specified by the `contentScript` option.

  @prop [contentScript] {string,array}
   This option specifies one or more content scripts to attach to targeted
   documents. Each script is supplied directly as a single string:

        var pageMod = require("page-mod");
        pageMod.PageMod({
          include: "*",
          contentScript: 'window.alert("Page matches ruleset");'
        });

   To attach multiple scripts, supply an array of strings.

   Content scripts specified by this option are loaded after those
   specified by the `contentScriptFile` option.

<div class="warning">
<p>Unless your content script is extremely simple and consists only of a
static string, don't use <code>contentScript</code>: if you do, you may
have problems getting your add-on approved on AMO.</p>
<p>Instead, keep the script in a separate file and load it using
<code>contentScriptFile</code>. This makes your code easier to maintain,
secure, debug and review.</p>
</div>

  @prop [contentScriptWhen="end"] {string}
   By default, content scripts are attached after all the content
   (DOM, JS, CSS, images) for the document has been loaded, at the time the
   [window.onload event](https://developer.mozilla.org/en/DOM/window.onload)
   fires. Using this option you can customize this behavior.

   The option takes a single string that may take any one of the following
   values:

   * `"start"`: load content scripts immediately after the document
   element is inserted into the DOM, but before the DOM content
   itself has been loaded
   * `"ready"`: load content scripts once DOM content has been loaded,
   corresponding to the
   [DOMContentLoaded](https://developer.mozilla.org/en/Gecko-Specific_DOM_Events)
   event
   * `"end"`: the default. Load content scripts once all the content
   (DOM, JS, CSS, images) has been loaded, at the time the
   [window.onload event](https://developer.mozilla.org/en/DOM/window.onload)
   fires

<!-- -->

       var pageMod = require("page-mod");
       pageMod.PageMod({
         include: "*",
         contentScript: 'window.alert("Page matches ruleset");',
         contentScriptWhen: "start"
       });

   If you specify `"start"` for `contentScriptWhen`, your scripts will not be
   able to interact with the document's DOM right away (although they could
   listen for `window.onload` or `DOMContentLoaded` themselves).

  @prop [contentScriptOptions] {object}
   You can use this option to define some read-only values for your content
   scripts.

   The option consists of an object literal listing `name:value` pairs for
   the values you want to provide to the content script. For example:

       var data = require("self").data;
       var pageMod = require("page-mod");
       pageMod.PageMod({
         include: "*",
         contentScriptFile: data.url("my-script.js"),
         contentScriptOptions: {
           showOptions: true,
           someNumbers: [1, 2],
           greeting: "Hello!"
         }
       });

   The values are accessible to content scripts via the `self.options`
   property:

       // my-script.js
       if (self.options.showOptions) {
         window.alert(self.options.greeting);
         window.alert(self.options.someNumbers[0] + self.options.someNumbers[1]);
       }

   The values can be any JSON-serializable value: a string, number,
   boolean, null, array of JSON-serializable values, or an object whose
   property values are themselves JSON-serializable. This means you can't send
   functions, and if the object contains methods they won't be usable. You
   also can't pass cyclic values.

  @prop [contentStyleFile] {string,array}
    Use this option to load one or more stylesheets into the targeted
    documents as
    [user stylesheets](https://developer.mozilla.org/en/CSS/Getting_Started/Cascading_and_inheritance).

    Each stylesheet is supplied as a separate file under your add-on's "data"
    directory, and is specified by a URL typically constructed using the
    `url()` method of the
    [`self` module's `data` object](modules/sdk/self.html#data).
    To add multiple stylesheet files, pass an array of URLs.

        var data = require("self").data;
        var pageMod = require("page-mod");

        pageMod.PageMod({
          include: "*.org",
          contentStyleFile: data.url("my-page-mod.css")
        });

    Content styles specified by this
    option are loaded before those specified by the `contentStyle` option.

    You can't currently use relative URLs in stylesheets loaded in this way.
    For example, consider a CSS file that references an external file like this:

        background: rgb(249, 249, 249) url('../../img/my-background.png') repeat-x top center;

    If you attach this file using `contentStyleFile`, "my-background.png"
    will not be found.

    As a workaround for this, you can build an absolute URL to a file in your
    "data" directory, and construct a `contentStyle` option embedding that URL
    in your rule. For example:

        var data = require("self").data;
        var pageMod = require("page-mod").PageMod({
          include: "*",
          contentStyleFile: data.url("my-style.css"),
          // contentStyle is built dynamically here to include an absolute URL
          // for the file referenced by this CSS rule.
          // This workaround is needed because we can't use relative URLs
          // in contentStyleFile or contentStyle.
          contentStyle: "h1 { background: url(" + data.url("my-pic.jpg") + ")}"
        });

    This add-on uses a separate file "my-style.css", loaded using
    `contentStyleFile`, for all CSS rules except those that reference
    an external file. For the rule that needs to refer to "my-pic.jpg",
    which is stored in the add-on's "data" directory, it uses `contentStyle`.

    Dynamically constructing code strings like those assigned to `contentScript`
    or `contentStyle` is usually considered an unsafe practice that may cause an
    add-on to fail AMO review. In this case it is safe, and should be allowed,
    but including a comment like that in the example above will help to
    prevent any misunderstanding.

  @prop [contentStyle] {string,array}
    Use this option to load one or more stylesheet rules into
    the targeted documents.

    Each stylesheet rule is supplied as a separate string. To supply
    multiple rules, pass an array of strings:

        var pageMod = require("page-mod");

        pageMod.PageMod({
          include: "*.org",
          contentStyle: [
            "div { padding: 10px; border: 1px solid silver}",
            "img { display: none}"
          ]
        });

    Content styles specified by this
    option are loaded after those specified by the `contentStyleFile` option.

  @prop [attachTo] {string,array}
   If this option is not specified, content scripts:

   * are not attached to any tabs that are already open when the page-mod is
   created.
   * are attached to all documents whose URL matches the rule: so if your
   rule matches a specific hostname and path, and the topmost document that
   satisfies the rule includes ten iframes using a relative URL, then your
   page-mod is applied eleven times.

<!-- -->

   You can modify this behavior using the `attachTo` option.

   It accepts the following values:

   * `"existing"`: the page-mod will be automatically applied on already
   opened tabs.
   * `"top"`: the page-mod will be applied to top-level tab documents
   * `"frame"`: the page-mod will be applied to all iframes inside tab
   documents

<!-- -->

   If the option is set at all, you must set at least one of `"top"` and
   `"frame"`.

   For example, the following page-mod will be attached to already opened
   tabs, but not to any iframes:

       var pageMod = require("page-mod");
       pageMod.PageMod({
         include: "*",
         contentScript: "",
         attachTo: ["existing", "top"],
         onAttach: function(worker) {
           console.log("attached to: " + worker.tab.url);
         }
       });

  @prop [onAttach] {function}
   Assign a listener function to this option to listen to the page-mod's
   `attach` event. See the
   [documentation for `attach`](modules/sdk/page-mod.html#attach) and
   [Communicating With Content Scripts](modules/sdk/page-mod.html#Communicating With Content Scripts).

</api>

<api name="include">
@property {List}
  A [list](modules/sdk/util/list.html) of match pattern strings.  These
  define the documents to which the page-mod applies. See the documentation of
  the `include` option above for details of `include` syntax.
  Rules can be added to the list by calling its
  `add` method and removed by calling its `remove` method.

</api>

<api name="destroy">
@method
  Stops the page-mod from making any more modifications. Once destroyed
  the page-mod can no longer be used.

  Modifications already made to open documents by content scripts
  will not be undone, but stylesheets added by `contentStyle` or
  `contentStyleFile`, will be unregistered immediately.
</api>

<api name="attach">
@event
  This event is emitted when the page-mod's content scripts are
  attached to a document whose URL matches the page-mod's `include` pattern.

   The listener function is passed a
   [`worker`](modules/sdk/content/worker.html) object that you
   can use to
   [communicate with the content scripts](modules/sdk/page-mod.html#Communicating With Content Scripts) your page-mod has
   loaded into this particular document.

   The `attach` event is triggered every time this page-mod's content
   scripts are attached to a document. So if the user loads several
   documents which match this page-mod's `include` pattern, `attach` will be
   triggered for each document, each time with a distinct `worker` instance.

   Each worker then represents a channel of communication with the set of
   content scripts loaded by this particular page-mod into that
   particular document.

@argument {Worker}
   The listener function is passed a [`Worker`](modules/sdk/content/worker.html)
   object that can be used to communicate with any content scripts
   attached to this document.
</api>

<api name="error">
@event
This event is emitted when an uncaught runtime error occurs in one of the
page-mod's content scripts.

@argument {Error}
Listeners are passed a single argument, the
[Error](https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Error)
object.
</api>

</api>
