` elements and Auto-Animate will animate all matching elements between the two. Here's a simple example to give you a better idea of how it can be used. The resulting animation will be the word "Magic" sliding 100px downwards. ```html

Magic

``` This example uses the `top` property to move the element but internally reveal.js will use a CSS transform to ensure smooth movement. This same approach to animation works with most animatable CSS properties meaning you can transition things like `position`, `font-size`, `line-height`, `color`, `background-color` and `padding`. #### How Elements are Matched When you navigate between two auto-animated slides we'll do our best to automatically find matching elements between the two slides. For text, we consider it a match if both the text contents and node type are identical. For images, videos and iframes we compare the `src` attribute. We also take into account the order in which the element appears in the DOM. In situations where automatic matching is not feasible you can give the objects that you want to animate between a matching `data-id` attribute. We prioritize matching `data-id` values above our automatic matching. Here's an example where we've given both blocks a matching ID since automatic matching has no content to go on. ```html

``` #### Animation Settings You can override specific animation settings such as easing and duration either for the whole presentation, per-slide or individually for each animated element. The following configuration attributes can be used to change the settings for a specific slide or element: | Attribute | Default | Description | :------------------------------- | ---------: | :---------- | data-auto-animate-easing | ease | A CSS [easing function](https://developer.mozilla.org/en-US/docs/Web/CSS/easing-function). | data-auto-animate-unmatched | true | Determines whether elements with no matching auto-animate target should fade in. Set to false to make them appear instantly. | data-auto-animate-duration | 1.0 | Animation duration in seconds. | data-auto-animate-delay | 0 | Animation delay in seconds (can only be set for specific elements, not at the slide level). If you'd like to change the defaults for the whole deck, use the following config options: ```javascript Reveal.initialize({ autoAnimateEasing: 'ease-out', autoAnimateDuration: 0.8, autoAnimateUnmatched: false }) ``` #### API: State Attributes and Events We add state attributes to the different elements involved in an auto-animation. These attributes can be tied into if you want to, for example, fine-tune the animation behavior with custom CSS. Right before an auto-animation starts we add `data-auto-animate="pending"` to the slide `

`. At this point the upcoming slide is visible and all of the animated elements have been moved to their starting positions. Next we switch to `data-auto-animate="running"` to indicate when the elements start animating towards their final properties. Each individual element is decorated with a `data-auto-animate-target` attribute. The value of the attribute is a unique ID for this particular animation OR "unmatched" if this element should animate as unmatched content. Each time a presentation navigates between two auto-animated slides it dispatches the `autoanimate` event. ```javascript Reveal.on( 'autoanimate', event => { // event.fromSlide, event.toSlide } ); ``` ### Vertical Slide Navigation Slides can be nested within other slides to create vertical stacks (see [Markup](#markup)). When presenting, you use the left/right arrows to step through the main (horizontal) slides. When you arrive at a vertical stack you can optionally press the up/down arrows to view the vertical slides or skip past them by pressing the right arrow. Here's an example showing a bird's-eye view of what this looks like in action:

#### Navigation Mode You can fine tune the reveal.js navigation behavior by using the `navigationMode` config option. Note that these options are only useful for presentations that use a mix of horizontal and vertical slides. The following navigation modes are available: | Value | Description | | :--------------------------- | :---------- | | default | Left/right arrow keys step between horizontal slides. Up/down arrow keys step between vertical slides. Space key steps through all slides (both horizontal and vertical). | | linear | Removes the up/down arrows. Left/right arrows step through all slides (both horizontal and vertical). | | grid | When this is enabled, stepping left/right from a vertical stack to an adjacent vertical stack will land you at the same vertical index.

Consider a deck with six slides ordered in two vertical stacks:
`1.1`    `2.1`
`1.2`    `2.2`
`1.3`    `2.3`

If you're on slide 1.3 and navigate right, you will normally move from 1.3 -> 2.1. With navigationMode set to "grid" the same navigation takes you from 1.3 -> 2.3. | ### Touch Navigation You can swipe to navigate through a presentation on any touch-enabled device. Horizontal swipes change between horizontal slides, vertical swipes change between vertical slides. If you wish to disable this you can set the `touch` config option to false when initializing reveal.js. If there's some part of your content that needs to remain accessible to touch events you'll need to highlight this by adding a `data-prevent-swipe` attribute to the element. One common example where this is useful is elements that need to be scrolled. ### Lazy Loading When working on presentation with a lot of media or iframe content it's important to load lazily. Lazy loading means that reveal.js will only load content for the few slides nearest to the current slide. The number of slides that are preloaded is determined by the `viewDistance` configuration option. To enable lazy loading all you need to do is change your `src` attributes to `data-src` as shown below. This is supported for image, video, audio and iframe elements. ```html

``` #### Lazy Loading Iframes Note that lazy loaded iframes ignore the `viewDistance` configuration and will only load when their containing slide becomes visible. Iframes are also unloaded as soon as the slide is hidden. When we lazy load a video or audio element, reveal.js won't start playing that content until the slide becomes visible. However there is no way to control this for an iframe since that could contain any kind of content. That means if we loaded an iframe before the slide is visible on screen it could begin playing media and sound in the background. You can override this behavior with the `data-preload` attribute. The iframe below will be loaded according to the `viewDistance`. ```html

``` You can also change the default globally with the `preloadIframes` configuration option. If set to `true` ALL iframes with a `data-src` attribute will be preloaded when within the `viewDistance` regardless of individual `data-preload` attributes. If set to `false`, all iframes will only be loaded when they become visible. ### Plugins **Outdated, this will be rewritten to match the 4.0 plugin API** Plugins should register themselves with reveal.js by calling `Reveal.registerPlugin( MyPlugin )`. Registered plugins _must_ expose a unique `id` property and can optionally expose an `init` function that reveal.js will call to initialize them. When reveal.js is booted up via `initialize()`, it will go through all registered plugins and invoke their `init` methods. If the `init` method returns a Promise, reveal.js will wait for that promise to be fulfilled before finishing the startup sequence and firing the [ready](#ready-event) event. Here’s an example of a plugin that does some asynchronous work before reveal.js can proceed: ```javascript let MyPlugin = { id: ’my-plugin’, init: deck => { return new Promise( resolve => setTimeout( resolve, 3000 ) ) } }; Reveal.initialize({ plugins: [ MyPlugin ] }).then( () => { console.log( ’Three seconds later...’ ) } ); ``` If the plugin’s init method does _not_ return a Promise, the plugin is considered ready right away and will not hold up the reveal.js startup sequence. ### Manually Registering Plugins TBD. Describe how plugins can be registered after reveal.js is already initialized. ### Retrieving Plugins If you want to check if a specific plugin is registered you can use the `Reveal.hasPlugin` method and pass in a plugin ID, for example: `Reveal.hasPlugin( ’my-plugin’ )`. If you want to retrieve a plugin instance you can use `Reveal.getPlugin( ’my-plugin’ )`. ### Dependencies Reveal.js doesn’t _rely_ on any third party scripts to work but a few optional libraries are included by default. These libraries are loaded as dependencies in the order they appear, for example: ```javascript Reveal.initialize({ dependencies: [ // Interpret Markdown in

elements { src: ’plugin/markdown/marked.js’, condition: () => { return !!document.querySelector( ’[data-markdown]’ ); } }, { src: ’plugin/markdown/markdown.js’, condition: () => { return !!document.querySelector( ’[data-markdown]’ ); } }, // Syntax highlight for

 elements
    { src: ’plugin/highlight/highlight.js’, async: true },

    // Zoom in and out with Alt+click
    { src: ’plugin/zoom-js/zoom.js’, async: true },

    // Speaker notes
    { src: ’plugin/notes/notes.js’, async: true },

    // MathJax
    { src: ’plugin/math/math.js’, async: true }
  ]
});
```

You can add your own extensions using the same syntax. The following properties are available for each dependency object:
- **src**: Path to the script to load
- **async**: [optional] Flags if the script should load after reveal.js has started, defaults to false
- **callback**: [optional] Function to execute when the script has loaded
- **condition**: [optional] Function which must return true for the script to be loaded

You can also include dependencies which are bundled/already present on the page. To include a bundled plugin. replace the `src` property with a reference to a `plugin` instance:
- **plugin**: the plugin instance (see [Plugins](#plugins))

### API

The `Reveal` object exposes a JavaScript API for controlling navigation and reading state:

```javascript
// Navigation
Reveal.slide( indexh, indexv, indexf );
Reveal.left();
Reveal.right();
Reveal.up();
Reveal.down();
Reveal.prev();
Reveal.next();
Reveal.prevFragment();
Reveal.nextFragment();

// Randomize the order of slides
Reveal.shuffle();

// Toggle presentation states, optionally pass true/false to force on/off
Reveal.toggleOverview();
Reveal.togglePause();
Reveal.toggleAutoSlide();

// Shows a help overlay with keyboard shortcuts, optionally pass true/false
// to force on/off
Reveal.toggleHelp();

// Change a config value at runtime
Reveal.configure({ controls: true });

// Returns the present configuration options
Reveal.getConfig();

// Fetch the current scale of the presentation
Reveal.getScale();

Reveal.getComputedSlideSize(); // Returns object with width, height keys, and (scaled) presentationWidth and presentationHeight.

// Retrieves the previous and current slide elements
Reveal.getPreviousSlide();
Reveal.getCurrentSlide();

Reveal.getIndices();        // { h: 0, v: 0, f: 0 }
Reveal.getSlidePastCount();
Reveal.getProgress();       // (0 == first slide, 1 == last slide)
Reveal.getSlides();         // Array of all slides
Reveal.getTotalSlides();    // Total number of slides

// Returns an array with all horizontal/vertical slides in the deck
Reveal.getHorizontalSlides();
Reveal.getVerticalSlides();

// Checks if the presentation contains two or more
// horizontal/vertical slides
Reveal.hasHorizontalSlides();
Reveal.hasVerticalSlides();

// Returns the speaker notes for the current slide
Reveal.getSlideNotes();

// State checks
Reveal.isFirstSlide();
Reveal.isLastSlide();
Reveal.isOverview();
Reveal.isPaused();
Reveal.isAutoSliding();

// Returns the top-level DOM element
Reveal.getRevealElement(); // ...
```

### Custom Key Bindings

Custom key bindings can be added and removed using the following Javascript API. Custom key bindings will override the default keyboard bindings, but will in turn be overridden by the user defined bindings in the ``keyboard`` config option.

```javascript
Reveal.addKeyBinding( binding, callback );
Reveal.removeKeyBinding( keyCode );
```

For example

```javascript
// The binding parameter provides the following properties
//      keyCode: the keycode for binding to the callback
//          key: the key label to show in the help overlay
//  description: the description of the action to show in the help overlay
Reveal.addKeyBinding( { keyCode: 84, key: 'T', description: 'Start timer' }, () => {
  // start timer
} )

// The binding parameter can also be a direct keycode without providing the help description
Reveal.addKeyBinding( 82, () => {
  // reset timer
} )
```

This allows plugins to add key bindings directly to Reveal so they can

* make use of Reveal's pre-processing logic for key handling (for example, ignoring key presses when paused); and
* be included in the help overlay (optional)

### Slide Change Events

A `slidechanged` event is fired each time the slide is changed. The event object holds the index values of the current slide as well as a reference to the previous and current slide DOM nodes.

Some libraries, like MathJax (see [#226](https://github.com/hakimel/reveal.js/issues/226#issuecomment-10261609)), get confused by the transforms and display states of slides. Often times, this can be fixed by calling their update or render function from this callback.

```javascript
Reveal.on( 'slidechanged', event => {
  // event.previousSlide, event.currentSlide, event.indexh, event.indexv
} );
```

The `slidechanged` event fires instantly when the slide changes. If you'd rather invoke your event listener when the slide has finished transitioning and is fully visible, you can use the `slidetransitionend` event. The `slidetransitionend` event includes the same event data as described above.

```javascript
Reveal.on( 'slidetransitionend', event => console.log( event.currentSlide ) );
```

### Presentation State

The presentation's current state can be fetched by using the `getState` method. A state object contains all of the information required to put the presentation back as it was when `getState` was first called. Sort of like a snapshot. It's a simple object that can easily be stringified and persisted or sent over the wire.

```javascript
Reveal.slide( 1 );
// we're on slide 1

var state = Reveal.getState();

Reveal.slide( 3 );
// we're on slide 3

Reveal.setState( state );
// we're back on slide 1
```

### Slide States

If you set `data-state="somestate"` on a slide ``, "somestate" will be applied as a class on the document element when that slide is opened. This allows you to apply broad style changes to the page based on the active slide.

Furthermore you can also listen to these changes in state via JavaScript:

```javascript
Reveal.on( 'somestate', () => {
  // TODO: Sprinkle magic
}, false );
```

### Slide Visibility
When preparing a presentation it can sometimes be helpful to prepare optional slides that you may or may not have time to show. This is easily done by appending a few slides at the end of the presentation, however this means that the reveal.js progress bar and slide numbering will hint that there are additional slides.

To "hide" those slides from reveal.js' numbering system you can add a `data-visibility` attribute to the slide like so ``.

### Slide Backgrounds

Slides are contained within a limited portion of the screen by default to allow them to fit any display and scale uniformly. You can apply full page backgrounds outside of the slide area by adding a `data-background` attribute to your `` elements. Four different types of backgrounds are supported: color, image, video and iframe.

#### Color Backgrounds

All CSS color formats are supported, including hex values, keywords, `rgba()` or `hsl()`.

```html

  Color

```

#### Image Backgrounds

By default, background images are resized to cover the full page. Available options:

| Attribute                        | Default    | Description |
| :------------------------------- | :--------- | :---------- |
| data-background-image            |            | URL of the image to show. GIFs restart when the slide opens. |
| data-background-size             | cover      | See [background-size](https://developer.mozilla.org/docs/Web/CSS/background-size) on MDN.  |
| data-background-position         | center     | See [background-position](https://developer.mozilla.org/docs/Web/CSS/background-position) on MDN. |
| data-background-repeat           | no-repeat  | See [background-repeat](https://developer.mozilla.org/docs/Web/CSS/background-repeat) on MDN. |
| data-background-opacity          | 1          | Opacity of the background image on a 0-1 scale. 0 is transparent and 1 is fully opaque. |

```html

  Image


  This background image will be sized to 100px and repeated

```

#### Video Backgrounds

Automatically plays a full size video behind the slide.

| Attribute                        | Default | Description |
| :---------------------------     | :------ | :---------- |
| data-background-video            |         | A single video source, or a comma separated list of video sources. |
| data-background-video-loop       | false   | Flags if the video should play repeatedly. |
| data-background-video-muted      | false   | Flags if the audio should be muted. |
| data-background-size             | cover   | Use `cover` for full screen and some cropping or `contain` for letterboxing. |
| data-background-opacity          | 1       | Opacity of the background video on a 0-1 scale. 0 is transparent and 1 is fully opaque. |

```html

  Video

```

#### Iframe Backgrounds

Embeds a web page as a slide background that covers 100% of the reveal.js width and height. The iframe is in the background layer, behind your slides, and as such it's not possible to interact with it by default. To make your background interactive, you can add the `data-background-interactive` attribute.

```html

  Iframe

```

Iframes are lazy-loaded when they become visible. If you'd like to preload iframes ahead of time, you can append a `data-preload` attribute to the slide ``. You can also enable preloading globally for all iframes using the `preloadIframes` configuration option.

#### Background Transitions

Backgrounds transition using a fade animation by default. This can be changed to a linear sliding transition by passing `backgroundTransition: 'slide'` to the `Reveal.initialize()` call. Alternatively you can set `data-background-transition` on any section with a background to override that specific transition.


### Parallax Background

If you want to use a parallax scrolling background, set the first two properties below when initializing reveal.js (the other two are optional).

```javascript
Reveal.initialize({

  // Parallax background image
  parallaxBackgroundImage: '', // e.g. "https://s3.amazonaws.com/hakim-static/reveal-js/reveal-parallax-1.jpg"

  // Parallax background size
  parallaxBackgroundSize: '', // CSS syntax, e.g. "2100px 900px" - currently only pixels are supported (don't use % or auto)

  // Number of pixels to move the parallax background per slide
  // - Calculated automatically unless specified
  // - Set to 0 to disable movement along an axis
  parallaxBackgroundHorizontal: 200,
  parallaxBackgroundVertical: 50

});
```

Make sure that the background size is much bigger than screen size to allow for some scrolling. [View example](http://revealjs.com/?parallaxBackgroundImage=https%3A%2F%2Fs3.amazonaws.com%2Fhakim-static%2Freveal-js%2Freveal-parallax-1.jpg¶llaxBackgroundSize=2100px%20900px).

### Slide Transitions

The global presentation transition is set using the `transition` config value. You can override the global transition for a specific slide by using the `data-transition` attribute:

```html

  This slide will override the presentation transition and zoom!



  Choose from three transition speeds: default, fast or slow!

```

You can also use different in and out transitions for the same slide:

```html

    The train goes on …


    and on …


    and stops.


    (Passengers entering and leaving)


    And it starts again.

```
You can choose from `none`, `fade`, `slide`, `convex`, `concave` and `zoom`.
### Internal links

It's easy to link between slides. The first example below targets the index of another slide whereas the second targets a slide with an ID attribute (``):

```html
Link
Link
```

You can also add relative navigation links, similar to the built in reveal.js controls, by appending one of the following classes on any element. Note that each element is automatically given an `enabled` class when it's a valid navigation route based on the current slide.

```html




 
 
```

### Fragments

Fragments are used to highlight individual elements on a slide. Every element with the class `fragment` will be stepped through before moving on to the next slide. Here's an example: http://revealjs.com/#/fragments

The default fragment style is to start out invisible and fade in. This style can be changed by appending a different class to the fragment:

```html

  grow
  shrink
  strike
  fade-out
  fade-up (also down, left and right!)
  fades in, then out when we move to the next step
  fades in, then obfuscate when we move to the next step
  blue only once
  highlight-red
  highlight-green
  highlight-blue

```

Multiple fragments can be applied to the same element sequentially by wrapping it, this will fade in the text on the first step and fade it back out on the second.

```html

  
    I'll fade in, then out
  

```

The display order of fragments can be controlled using the `data-fragment-index` attribute.

```html

  Appears last
  Appears first
  Appears second

```

### Fragment events

When a slide fragment is either shown or hidden reveal.js will dispatch an event.

Some libraries, like MathJax (see #505), get confused by the initially hidden fragment elements. Often times this can be fixed by calling their update or render function from this callback.

```javascript
Reveal.on( 'fragmentshown', event => {
  // event.fragment = the fragment DOM element
} );
Reveal.on( 'fragmenthidden', event => {
  // event.fragment = the fragment DOM element
} );
```

### Code Syntax Highlighting

By default, Reveal is configured with [highlight.js](https://highlightjs.org/) for code syntax highlighting. To enable syntax highlighting, you'll have to load the highlight plugin ([plugin/highlight/highlight.js](plugin/highlight/highlight.js)) and a highlight.js CSS theme (Reveal comes packaged with the Monokai themes: [lib/css/monokai.css](lib/css/monokai.css)).

```javascript
Reveal.initialize({
  // More info https://github.com/hakimel/reveal.js#dependencies
  dependencies: [
    { src: 'plugin/highlight/highlight.js', async: true },
  ]
});
```

Below is an example with clojure code that will be syntax highlighted. When the `data-trim` attribute is present, surrounding whitespace is automatically removed.  HTML will be escaped by default. To avoid this, for example if you are using `` to call out a line of code, add the `data-noescape` attribute to the `` element.

```html

  
(def lazy-fib
  (concat
   [0 1]
   ((fn rfib [a b]
        (lazy-cons (+ a b) (rfib b (+ a b)))) 0 1)))
  

```

#### Line Numbers & Highlights

To enable line numbers, add `data-line-numbers` to your `` tags. If you want to highlight specific lines you can provide a comma separated list of line numbers using the same attribute. For example, in the following example lines 4 and 8-11 are highlighted:

```html

import React, { useState } from 'react';
 
function Example() {
  const [count, setCount] = useState(0);
 
  return (
    
      You clicked {count} times
      
    
  );
}

```



#### Step-by-step Highlights

You can step through multiple code highlights on the same code block. Delimit each of your highlight steps with the `|` character. For example `data-line-numbers="1|2-3|4,6-10"` will produce three steps. It will start by highlighting line 1, next step is lines 2-3, and finally line 4 and 6 through 10.



### Slide number

If you would like to display the page number of the current slide you can do so using the `slideNumber` and `showSlideNumber` configuration values.

```javascript
// Shows the slide number using default formatting
Reveal.configure({ slideNumber: true });

// Slide number formatting can be configured using these variables:
//  "h.v":  horizontal . vertical slide number (default)
//  "h/v":  horizontal / vertical slide number
//    "c":  flattened slide number
//  "c/t":  flattened slide number / total slides
Reveal.configure({ slideNumber: 'c/t' });

// You can provide a function to fully customize the number:
Reveal.configure({ slideNumber: slide => {
    // Ignore numbering of vertical slides
    return [ Reveal.getIndices( slide ).h ];
}});

// Control which views the slide number displays on using the "showSlideNumber" value:
//     "all": show on all views (default)
// "speaker": only show slide numbers on speaker notes view
//   "print": only show slide numbers when printing to PDF
Reveal.configure({ showSlideNumber: 'speaker' });
```

### Overview mode

Press »ESC« or »O« keys to toggle the overview mode on and off. While you're in this mode, you can still navigate between slides,
as if you were at 1,000 feet above your presentation. The overview mode comes with a few API hooks:

```javascript
Reveal.on( 'overviewshown', event => { /* ... */ } );
Reveal.on( 'overviewhidden', event => { /* ... */ } );

// Toggle the overview mode programmatically
Reveal.toggleOverview();
```

### Fullscreen mode

Just press »F« on your keyboard to show your presentation in fullscreen mode. Press the »ESC« key to exit fullscreen mode.

### Embedded media

Add `data-autoplay` to your media element if you want it to automatically start playing when the slide is shown:

```html

```

If you want to enable or disable autoplay globally, for all embedded media, you can use the `autoPlayMedia` configuration option. If you set this to `true` ALL media will autoplay regardless of individual `data-autoplay` attributes. If you initialize with `autoPlayMedia: false` NO media will autoplay.

Note that embedded HTML5 `

Magic

Magic

Color

Image

This background image will be sized to 100px and repeated

Video

Iframe

This slide will override the presentation transition and zoom!

Choose from three transition speeds: default, fast or slow!

This video will use up the remaining space on the slide