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This is part of the VimFx documentation.
Copyright Simon Lydell 2015, 2016.
See the file README.md for copying conditions.
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# API

VimFx has an API. It is intended to be used by users who would like to write a
so-called [config file].

## Getting the API

```js
let {classes: Cc, interfaces: Ci, utils: Cu} = Components
Cu.import('resource://gre/modules/Services.jsm')
let apiPref = 'extensions.VimFx.api_url'
let apiUrl = Services.prefs.getComplexValue(apiPref, Ci.nsISupportsString).data
Cu.import(apiUrl, {}).getAPI(vimfx => {

  // Do things with the `vimfx` object here.

})
```

You might also want to take a look at the [config file bootstrap.js
example][bootstrap.js].

Note that the callback passed to `getAPI` is called once every time VimFx starts
up, not once per Firefox session! This means that if you update VimFx (or
disable and then enable it), the callback is re-run with the new version.


## API

The following sub-sections assume that you store VimFx’s API in a variable
called `vimfx`.

### `vimfx.get(pref)`, `vimfx.getDefault(pref)` and `vimfx.set(pref, value)`

Gets or sets the (default) value of the VimFx pref `pref`.

You can see all prefs in [defaults.coffee], or by opening [about:config] and
filtering by `extensions.vimfx`. Note that you can also access the [special
options], which may not be accessed in [about:config], using `vimfx.get()` and
`vimfx.set()`—in fact, this is the _only_ way of accessing those options.

#### `vimfx.get(pref)`

Gets the value of the VimFx pref `pref`.

```js
// Get the value of the Hint chars option:
vimfx.get('hint_chars')
// Get all keyboard shortcuts (as a string) for the `f` command:
vimfx.get('mode.normal.follow')
```

#### `vimfx.getDefault(pref)`

Gets the default value of the VimFx pref `pref`.

Useful when you wish to extend a default, rather than replacing it. See below.

#### `vimfx.set(pref, value)`

Sets the value of the VimFx pref `pref` to `value`.

```js
// Set the value of the Hint chars option:
vimfx.set('hint_chars', 'abcdefghijklmnopqrstuvwxyz')
// Add yet a keyboard shortcut for the `f` command:
vimfx.set('mode.normal.follow', vimfx.getDefault('mode.normal.follow') + '  e')
```

When extending a pref (as in the second example above), be sure to use
`vimfx.getDefault` rather than `vimfx.get`. Otherwise you get a multiplying
effect. In the above example, after starting Firefox a few times the pref would
be `f  e  e  e  e`. Also, if you find that example very verbose: Remember that
you’re using a programming language! Write a small helper function that suits
your needs.

Note: If you produce conflicting keyboard shortcuts, the order of your code does
not matter. The command that comes first in VimFx’s settings page in the Add-ons
Manager (and in the Keyboard Shortcuts help dialog) gets the shortcut; the other
one(s) do(es) not. See the notes about order in [mode object], [category object]
and [command object] for more information about order.

```js
// Even though we set the shortcut for focusing the search bar last, the command
// for focusing the location bar “wins”, because it comes first in VimFx’s
// settings page in the Add-ons Manager.
vimfx.set('mode.normal.focus_location_bar', 'ö')
vimfx.set('mode.normal.focus_search_bar', 'ö')

// Swapping their orders also swaps the “winner”.
let {commands} = vimfx.modes.normal
;[commands.focus_location_bar.order, commands.focus_search_bar.order] =
  [commands.focus_search_bar.order, commands.focus_location_bar.order]
```

### `vimfx.addCommand(options, fn)`

Creates a new command.

`options`:

- name: `String`. The name used when accessing the command via
  `vimfx.modes[options.mode].commands[options.name]`. It is also used for the
  pref used to store the shortcuts for the command:
  `` `custom.mode.${options.mode}.${options.name}` ``.
- description: `String`. Shown in the Keyboard Shortcuts help dialog and VimFx’s
  settings page in the Add-ons Manager.
- mode: `String`. Defaults to `'normal'`. The mode to add the command to. The
  value has to be one of the keys of [`vimfx.modes`].
- category: `String`. Defaults to `'misc'` for Normal mode and `''`
  (uncategorized) otherwise. The category to add the command to. The
  value has to be one of the keys of [`vimfx.get('categories')`][categories].
- order: `Number`. Defaults to putting the command at the end of the category.
  The first of the default commands has the order `100` and then they increase
  by `100` per command. This allows to put new commands between two already
  existing ones.

`fn` is called when the command is activated. See the [onInput] documentation
below for more information.

<strong id="custom-command-shortcuts">Note</strong> that you have to give the
new command a shortcut in VimFx’s settings page in the Add-ons Manager or set
one using `vimfx.set()` to able to use the new command.

```js
vimfx.addCommand({
  name: 'hello',
  description: 'Log Hello World',
}, => {
  console.log('Hello World!')
})
// Optional:
vimfx.set('custom.mode.normal.hello', 'gö')
```

### `vimfx.addOptionOverrides(...rules)` and `vimfx.addKeyOverrides(...rules)`

These methods take any number of arguments. Each argument is a rule. The rules
are added in order. The methods may be run multiple times.

A rule is an `Array` of length 2:

1. The first item is a function that returns `true` if the rule should be
   applied and `false` if not. This is called the matching function.
2. The second item is the value that should be used if the rule is applied. This
   is called the override.

The rules are tried in the same order they were added. When a matching rule is
found it is applied. No more rules will be applied.

#### `vimfx.addOptionOverrides(...rules)`

The rules are matched any time the value of a VimFx pref is needed.

The matching function receives a [location object].

The override is an object whose keys are VimFx pref names and whose values
override the pref in question. The values should be formatted as in an [options
object].

```js
vimfx.addOptionOverrides(
  [ ({hostname, pathname, hash}) =>
    `${hostname}${pathname}${hash}` === 'google.com/',
    {prevent_autofocus: false}
  ]
)
```

#### `vimfx.addKeyOverrides(...rules)`

The rules are matched any time you press a key that is not part of the tail of a
multi-key shortcut.

The matching function receives a [location object] as well as the current
mode name (one of the keys of [`vimfx.modes`]).

The override is an array of keys which should not activate VimFx commands but be
sent to the page.

This allows to disable commands on specific sites. To _add_ commands on specific
sites, add them globally and then disable them on all _other_ sites.

```js
vimfx.addKeyOverrides(
  [ location => location.hostname === 'facebook.com',
    ['j', 'k']
  ]
)
```

### `vimfx.on(eventName, listener)`

Runs `listener(data)` when `eventName` is fired.

#### The `locationChange` event

Occurs when opening a new tab, navigating to a new URL or refreshing the page,
causing a full page load. The data passed to listeners is an object with the
following properties:

- vim: The current [vim object].
- location: A [location object].

This can be used to enter a different mode by default on some pages (which can
be used to replace the blacklist option).

```js
vimfx.on('locationChange', ({vim, location}) => {
  if (location.hostname === 'example.com') {
    vim.enterMode('ignore')
  }
})
```

#### The `notification` and `hideNotification` events

The `notification` event occurs when `vim.notify(message)` is called, and means
that `message` should be displayed to the user.

The `hideNotification` event occurs when the `vim.hideNotification()` is called,
and means that the current notification is requested to be hidden.

The data passed to listeners is an object with the following properties:

- vim: The current [vim object].
- message: The message that should be notified. Only for the `notification`
  event.

Both of these events are emitted even if the [`notifications_enabled`] option is
disabled, allowing you to display notifications in any way you want.

#### The `modeChange` event

Occurs whenever the current mode in any tab changes. The initial entering of the
default mode in new tabs also counts as a mode change. The data passed to
listeners is the current [vim object].

```js
vimfx.on('modeChange', vim => {
  let mode = vimfx.modes[vim.mode].name
  vim.notify(`Entering mode: ${mode}`)
})
```

#### The `TabSelect` event

Occurs whenever any tab in any window is selected. This is also fired when
Firefox starts for the currently selected tab. The data passed to listeners is
the `event` object passed to the standard Firefox [TabSelect] event.

### The `modeDisplayChange` event

This is basically a combination of the `modeChange` and the `TabSelect` events.
The event is useful for knowing when to update UI showing the current mode. The
data passed to listeners is the current [vim object].

(VimFx itself uses this event to update the toolbar [button], by setting
`#main-window[vimfx-mode]` to the current mode. You may use this with custom
[styling].)

#### The `focusTypeChange` event

Occurs when focusing or blurring any element. The data passed to listeners is an
object with the following properties:

- vim: The current [vim object].
- focusType: A string similar to `match.focus` of a [match object], with the
  following differences:

  - The current pressed key is _not_ taken into account, because focus and blur
    events have no current key.
  - The value is never `null` or `'other'`, but `'none'` instead.

(VimFx itself uses this event to update the toolbar [button], by setting
`#main-window[vimfx-focus-type]` to the current focus type. You may use this
with custom [styling].)



### `vimfx.modes`

An object whose keys are mode names and whose values are [mode object]s.

This is a very low-level part of the API. It allows to:

- Access all commands and run them. This is the most common thing that a config
  file user needs it for.

  ```js
    let {commands} = vimfx.modes.normal
    // Inside a custom command:
    commands.tab_new.run(args)
  ```

- Adding new commands. It is recommended to use the `vimfx.addCommand()` helper
  instead. It’s easier.

  ```js
  vimfx.modes.normal.commands.new_command = {
    pref: 'extensions.my_extension.mode.normal.new_command',
    category: 'misc',
    order: 10000,
    description: translate('mode.normal.new_command'),
    run: args => console.log('New command! args:', args)
  }
  ```

- Adding new modes. This is the most advanced customization you can do to VimFx.
  Expect having to read VimFx’s source code to figure it all out.

  ```js
  vimfx.modes.new_mode = {
    name: () => translate('mode.new_mode'),
    order: 10000,
    commands: {},
    onEnter(args) {},
    onLeave(args) {},
    onInput(args, match) {
      if (match.type === 'full') {
        match.command.run(args)
      }
      return (match.type !== 'none')
    },
  }
  ```

Have a look at [modes.coffee] and [commands.coffee] for more information.

### `vimfx.get('categories')`

An object whose keys are category names and whose values are [category object]s.

```js
let categories = vimfx.get('categories')

// Add a new category.
categories.custom = {
  name: () => 'Custom commands',
  order: 10000,
}

// Swap the order of the Location and Tabs categories.
;[commands.focus_location_bar.order, categories.tabs.order] =
  [categories.tabs.order, commands.focus_location_bar.order]
```

### Mode object

A mode is an object with the following properties:

- name: `String`. A human readable name of the mode used in the Keyboard
  Shortcuts help dialog and VimFx’s settings page in the Add-ons Manager. Config
  file users adding custom modes could simply use a hard-coded string; extension
  authors are encouraged to look up the name from a locale file.
- order: `Number`. The first of the default modes has the order `100` and then
  they increase by `100` per mode. This allows to put new modes between two
  already existing ones.
- commands: `Object`. The keys are command names and the values are [command
  object]s.
- onEnter(data, ...args): `Function`. Called when the mode is entered.
- onLeave(data): `Function`. Called when the mode is left.
- onInput(data, match): `Function`. Called when a key is pressed.

#### onEnter, onLeave and onInput

These methods are called with an object (called `data` above) with the following
properties:

- vim: The current [vim object].
- storage: An object unique to the current [vim object] and to the current mode.
  Allows to share things between commands of the same mode by getting and
  setting keys on it.

##### onEnter

This method is called with an object as mentioned above, and after that there
may be any number of arguments (`args` in `vim.enterMode(modeName, ...args)`)
that the mode is free to do whatever it wants with.

Whatever is returned from `onEnter` will be returned from
`vim.enterMode(modeName, ...args)`.

##### onInput

The object passed to this method (see above) also has the following properties:

- uiEvent: `Event` or `false`. The keydown event object if the event occurred in
  the browser UI, `false` otherwise (if the event occurred in web page content).
- count: `Number`. The count for the command. `undefined` if no count. (This is
  simply a copy of `match.count`. `match` is defined below.)

The above object should be passed to commands when running them. The mode is
free to do whatever it wants with the return value (if any) of the commands it
runs.

It also receives a [match object] as the second argument.

`onInput` should return `true` if the current keypress should not be passed on
to the browser and web pages, and `false` otherwise.

### Category object

A category is an object with the following properties:

- name: `String`. A human readable name of the category used in the Keyboard
  Shortcuts help dialog and VimFx’s settings page in the Add-ons Manager. Config
  file users adding custom categories could simply a use hard-coded string;
  extension authors are encouraged to look up the name from a locale file.
- order: `Number`. The first of the default categories is the “uncategorized”
  category. It has the order `100` and then they increase by `100` per category.
  This allows to put new categories between two already existing ones.

### Command object

A command is an object with the following properties:

- pref: `String`. The pref used to store the shortcuts for the command.
- run(args): `Function`. Called when the command is activated.
- description: `String`. A description of the command, shown in the Keyboard
  Shortcuts help dialog and VimFx’s settings page in the Add-ons Manager. Config
  file users adding custom commands could simply use a hard-coded string;
  extension authors are encouraged to look up the name from a locale file.
- category: `String`. The category to add the command to. The value has to be
  one of the keys of [`vimfx.get('categories')`][categories].
- order: `Number`. The first of the default commands has the order `100` and
  then they increase by `100` per command. This allows to put new commands
  between two already existing ones.

### Match object

A `match` object has the following properties:

- type: `String`. It has one of the following values:

  - `'full'`: The current keypress, together with previous keypresses, fully
    matches a command shortcut.
  - `'partial'`: The current keypress, together with previous keypresses,
    partially matches a command shortcut.
  - `'count'`: The current keypress is not part of a command shortcut, but is a
    digit and contributes to the count of a future matched command.
  - `'none'`: The current keypress is not part of a command shortcut and does
    not contribute to a count.

- focus: `String` or `null`. The type of currently focused _element_ plus
  current pressed _key_ combo. You might not want to run commands and suppress
  the event if this value is anything other than null. It has one of the
  following values, depending on what kind of _element_ is focused and which
  _key_ was pressed:

  - `'editable'`: element: some kind of text input, a `<select>` element or a
    “contenteditable” element. key: any pressed key.
  - `'activatable'`: element: an “activatable” element (link or button).
    key: see the [`activatable_element_keys`] option.
  - `'adjustable'`: element: an “adjustable” element (form control or video
    player). key: see the [`adjustable_element_keys`] option.
  - `'other'`: element: some other kind of element that can receive keystrokes,
    for example an element in fullscreen mode. key: any pressed key.

  If none of the above criteria is met, the value is `null`, which means that
  the currently focused element does not appear to respond to keystrokes in any
  special way.

- command: `null` unless `type` is `'full'`. Then it is the matched command (a
  [command object]).

  The matched command should usually be run at this point. It is suitable to
  pass on the object passed to [onInput] to the command. Some modes might choose
  to add extra properties to the object first. (That is favored over passing
  several arguments, since it makes it easier for the command to in turn pass
  the same data it got on to another command, if needed.)

  Usually the return value of the command isn’t used, but that’s up to the mode.

- count: `Number`. The count for the command. `undefined` if no count.

- specialKeys: `Object`. The keys may be any of the following:

  - `<force>`
  - `<late>`

  If a key exists, its value is always `true`. The keys that exist indicate the
  [special keys] for the sequence used for the matched command (if any).

- keyStr: `String`. The current keypress represented as a string.

- unmodifiedKey: `String`. `keyStr` without modifiers.

- toplevel: `Boolean`. Whether or not the match was a toplevel match in the
  shortcut key tree. This is `true` unless the match is part of the tail of a
  multi-key shortcut.

- discard(): `Function`. Discards keys pressed so far: If `type` is `'partial'`
  or `'count'`. For example, if you have typed `12g`, run `match.discard()` and
  then press `$`, the `$` command will be run instead of `12g$`.

### Vim object

There is one `vim` object per tab.

A `vim` object has the following properties:

- window: [`Window`]. The current Firefox window object. Most commands
  interacting with Firefox’s UI use this.

- browser: [`Browser`]. The `browser` that this vim object handles.

- options: `Object`. Provides access to all of VimFx’s options. It is an
  [options object].

- mode: `String`. The current mode name.

- enterMode(modeName, ...args): `Function`. Enter mode `modeName`, passing
  `...args` to the mode. It is up to every mode to do whatever it wants to with
  `...args`. If `modeName` was already the current mode, nothing is done and
  `undefined` is returned. Otherwise it us up to the mode to return whatever it
  wants to.

- isUIEvent(event): `Function`. Returns `true` if `event` occurred in the
  browser UI, and `false` otherwise (if it occurred in web page content).

- notify(message): `Function`. Display a notification with the text `message`.

- hideNotification(): `Function`. Hide the current notification (if any).

- markPageInteraction(value=true): `Function`. When `value` is `true` (as it is
  by default when the argument is omitted), marks that the user has interacted
  with the page. After that [autofocus prevention] is not done anymore. Commands
  interacting with web page content might want to do this. If `value` is
  `false`, the state is reset and autofocus prevention _will_ be done again.

**Warning:** There are also properties starting with an underscore on `vim`
objects. They are private, and not supposed to be used outside of VimFx’s own
source code. They may change at any time.

### Options object

An `options` object provides access to all of VimFx’s options. It is an object
whose keys are VimFx pref names.

Note that the values are not just simply `vimfx.get(pref)` for the `pref` in
question; they are _parsed_ (`parse(vimfx.get(pref))`):

- Space-separated prefs are parsed into arrays of strings.

- `black_list` and `{prev,next}_patterns` are parsed into arrays of regular
  expressions.

(See [parse-prefs.coffee] for all details.)

Any [option overrides] are automatically taken into account when getting an
option value.

The [special options] are also available on this object.


### Location object

A location object is very similar to [`window.location`] in web pages.
Technically, it is a [`URL`] instance. You can experiment with the current
location object by opening the [web console] and entering `location`.


## Frame script API

In frame scripts, the API consists of assigning global variables prefixed with
`VimFx`. VimFx then uses these when needed.

```js
this.VimFxSomething = ...
```

### `VimFxHintMatcher(...)`

If available, it is used to let you customize which elements do and don’t get
hints. It might help to read about [the `f` commands] first.

```js
this.VimFxHintMatcher = (id, element, {type, semantic}) => {
  // Inspect `element` and change `type` and `semantic` if needed.
  return {type, semantic}
}
```

The arguments passed to this function are:

- id: `String`. A string identifying which command is used:

  - `'normal'`: `f` or `af`.
  - `'tab'`: `F`, `gf` or `gF`.
  - `'copy'`: `yf`.
  - `'focus'`: `zf`.

- element: `Element`. One out of all elements currently inside the viewport.

- info: `Object`. It has the following properties:

  - type: `String` or `null`. If a string, it means that `element` should get a
    hint. If `null`, it won’t. See the available strings below. When a marker
    is matched, `type` decides what happens to `element`.
  - semantic: `Boolean`. Indicates whether or not the element is “semantic.”
    Semantic elements get better hints.

  This object contains information on how VimFx has matched `element`. You have
  the opportunity to change this.

The available type strings depend on `id`:

- normal:

  - link: A “proper” link (not used as a button with the help of JavaScript),
    with an `href` attribute.
  - text: An element that can you can type in, such as text inputs.
  - clickable: Some clickable element not falling into another category.
  - clickable-special: Like “clickable,” but uses a different technique to
    simulate a click on the element. If “clickable” doesn’t work, try this one.
  - scrollable: A scrollable element.

- tab:

  - link: Like “link” when `id` is “normal” (see above).

- copy:

  - link: Like “link” when `id` is “normal” (see above).
  - text: Like “text” when `id` is “normal” (see above), except that in this
    case “contenteditable” elements are not included.
  - contenteditable: Elements with “contenteditable” turned on.

- focus:

  - focusable: Any focusable element not falling into another category.
  - scrollable: Like “scrollable” when `id` is “normal” (see above).

The function must return an object like the `info` parameter (with the `type`
and `semantic` properties).


## Stability

The API is currently **experimental** and therefore **unstable.** Things might
break with new VimFx versions. However, no breaking changes are planned, and
will be avoided if feasible.

As soon as VimFx 1.0.0 (which does not seem to be too far away) is released
backwards compatibility will be a priority and won’t be broken until VimFx
2.0.0.

[option overrides]: #vimfxaddoptionoverridesrules
[categories]: #vimfxgetcategories
[`vimfx.modes`]: #vimfxmodes
[onInput]: #oninput
[mode object]: #mode-object
[category object]: #category-object
[command object]: #command-object
[match object]: #match-object
[vim object]: #vim-object
[options object]: #options-object
[location object]: #location-object

[blacklisted]: options.md#blacklist
[special options]: options.md#special-options
[config file]: config-file.md
[bootstrap.js]: config-file.md#bootstrapjs
[autofocus prevention]: options.md#prevent-autofocus
[`activatable_element_keys`]: options.md#activatable_element_keys
[`adjustable_element_keys`]: options.md#adjustable_element_keys
[`notifications_enabled`]: options.md#notifications_enabled

[button]: button.md
[the `f` commands]: commands.md#the-f-commands--hints-mode
[special keys]: shortcuts.md#special-keys
[styling]: styling.md

[defaults.coffee]: ../extension/lib/defaults.coffee
[parse-prefs.coffee]: ../extension/lib/parse-prefs.coffee
[modes.coffee]: ../extension/lib/modes.coffee
[commands.coffee]: ../extension/lib/commands.coffee
[vim.coffee]: ../extension/lib/vim.coffee

[`Window`]: https://developer.mozilla.org/en-US/docs/Web/API/Window
[`Browser`]: https://developer.mozilla.org/en-US/docs/Mozilla/Tech/XUL/browser
[`window.location`]: https://developer.mozilla.org/en-US/docs/Web/API/Location
[`URL`]: https://developer.mozilla.org/en-US/docs/Web/API/URL
[TabSelect]: https://developer.mozilla.org/en-US/docs/Web/Events/TabSelect
[web console]: https://developer.mozilla.org/en-US/docs/Tools/Web_Console
[about:config]: http://kb.mozillazine.org/About:config