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Introduce plugin framework

Browse Source 
* Source files are under src/
* js/impress.js is now generated, but remains part of the repo (so it just works)
* npm run build
* build.js uses buildify node module
* Break out navigation and resize plugins from core src/impress.js file
This commit is contained in:
Henrik Ingo
2017-09-25 03:01:58 +03:00
parent c58b7b8a44
commit 0dc8b43650
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Impress.js Plugins documentation
================================
The default set of plugins
--------------------------
A lot of impress.js features are and will be implemented as plugins. Each plugin
has user documentation in a README.md file in [its own directory](./).
The plugins in this directory are called default plugins, and - unsurprisingly -
are enabled by default. However, most of them won't do anything by default,
rather require the user to invoke them somehow. For example:
* The *navigation* plugin waits for the user to press some keys, arrows, page
down, page up, space or tab.
* The *autoplay* plugin looks for the HTML attribute `data-autoplay` to see
whether it should do its thing.
* The *toolbar* plugin looks for a `<div>` element to become visible.
Extra addons
------------
Yet more features are available in presentations that enable
[extra addons](../../extras/). Extra addons are 3rd party plugins integrated
into impress.js to provide convenient and standardized access to them. However,
they are not activated by default, rather must be included with a `<script>`
tag.
Note: The enabled extra addons are automatically initialized by the *extras*
plugin.
Example HTML and CSS
--------------------
Generally plugins will do something sane, or nothing, by default. Hence, no
particular HTML or CSS is required. The README file of each plugin documents the
HTML and CSS that you can use with that plugin.
For your convenience, below is some sample HTML and CSS code covering all the
plugins that you may want to use or adapt.
### Sample HTML to enable plugins and extra addons
<head>
<!-- CSS files if using Highlight.js or Mermaid.js extras. -->
<link rel="stylesheet" href="../../extras/highlight/styles/github.css">
<link rel="stylesheet" href="../../extras/mermaid/mermaid.forest.css">
</head>
<body>
<div id="impress" data-autoplay="10">
<div class="step"
data-autoplay="15"
data-rel-x="1000"
data-rel-y="1000">
<h1>Slide content</h1>
<ul>
<li class="substep">Point 1</li>
<li class="substep">Point 2</li>
</ul>
<div class="notes">
Speaker notes are shown in the impressConsole.
</div>
</div>
</div>
<div id="impress-toolbar"></div>
<div class="impress-progressbar"><div></div></div>
<div class="impress-progress"></div>
<div id="impress-help"></div>
<script type="text/javascript" src="../../extras/highlight/highlight.pack.js"></script>
<script type="text/javascript" src="../../extras/mermaid/mermaid.min.js"></script>
<script type="text/javascript" src="../../extras/markdown/markdown.js"></script>
<script type="text/javascript" src="../../extras/mathjax/MathJax.js?config=TeX-AMS_CHTML"></script>
</body>
### Sample CSS related to plugins and extra addons
/* Using the substep plugin, hide bullet points at first, then show them one by one. */
#impress .step .substep {
opacity: 0;
}
#impress .step .substep.substep-visible {
opacity: 1;
transition: opacity 1s;
}
/*
Speaker notes allow you to write comments within the steps, that will not
be displayed as part of the presentation. However, they will be picked up
and displayed by impressConsole.js when you press P.
*/
.notes {
display: none;
}
/* Toolbar plugin */
.impress-enabled div#impress-toolbar {
position: fixed;
right: 1px;
bottom: 1px;
opacity: 0.6;
z-index: 10;
}
.impress-enabled div#impress-toolbar > span {
margin-right: 10px;
}
.impress-enabled div#impress-toolbar.impress-toolbar-show {
display: block;
}
.impress-enabled div#impress-toolbar.impress-toolbar-hide {
display: none;
}
/* If you disable pointer-events (like in the impress.js official demo), you need to re-enable them for the toolbar. */
.impress-enabled #impress-toolbar { pointer-events: auto }
/* Progress bar */
.impress-enabled .impress-progressbar {
position: absolute;
right: 318px;
bottom: 1px;
left: 118px;
border-radius: 7px;
border: 2px solid rgba(100, 100, 100, 0.2);
}
.impress-enabled .impress-progressbar DIV {
width: 0;
height: 2px;
border-radius: 5px;
background: rgba(75, 75, 75, 0.4);
transition: width 1s linear;
}
.impress-enabled .impress-progress {
position: absolute;
left: 59px;
bottom: 1px;
text-align: left;
opacity: 0.6;
}
.impress-enabled #impress-help {
background: none repeat scroll 0 0 rgba(0, 0, 0, 0.5);
color: #EEEEEE;
font-size: 80%;
position: fixed;
left: 2em;
bottom: 2em;
width: 24em;
border-radius: 1em;
padding: 1em;
text-align: center;
z-index: 100;
font-family: Verdana, Arial, Sans;
}
.impress-enabled #impress-help td {
padding-left: 1em;
padding-right: 1em;
}
For developers
==============
The vision for impress.js is to provide a compact core library doing the
actual presentations, with a collection of plugins that provide additional
functionality. A default set of plugins are distributed together with the core
impress.js, and are located in this directory. They are called *default plugins*
because they are distributed and active when users use the [js/impress.js](../../js/impress.js)
in their presentations.
Building js/impress.js
-----------------------
The common way to use impress.js is to link to the file
[js/impress.js](../../js/impress.js). This is a simple concatenation of the
core impress.js and all plugins in this directory. If you edit or add code
under [src/](../), you can run `node build.js` to recreate the distributable
`js/impress.js` file. The build script also creates a minified file, but this
is not included in the git repository.
### Tip: Build errors
If your code has parse errors, the `build.js` will print a rather unhelpful
exception like
/home/hingo/hacking/impress.js/js/impress.js
/home/hingo/hacking/impress.js/node_modules/uglify-js/lib/parse-js.js:271
throw new JS_Parse_Error(message, line, col, pos);
^
Error
at new JS_Parse_Error (/home/hingo/hacking/impress.js/node_modules/uglify-js/lib/parse-js.js:263:18)
at js_error (/home/hingo/hacking/impress.js/node_modules/uglify-js/lib/parse-js.js:271:11)
at croak (/home/hingo/hacking/impress.js/node_modules/uglify-js/lib/parse-js.js:733:9)
at token_error (/home/hingo/hacking/impress.js/node_modules/uglify-js/lib/parse-js.js:740:9)
at unexpected (/home/hingo/hacking/impress.js/node_modules/uglify-js/lib/parse-js.js:746:9)
at Object.semicolon [as 1] (/home/hingo/hacking/impress.js/node_modules/uglify-js/lib/parse-js.js:766:43)
at prog1 (/home/hingo/hacking/impress.js/node_modules/uglify-js/lib/parse-js.js:1314:21)
at simple_statement (/home/hingo/hacking/impress.js/node_modules/uglify-js/lib/parse-js.js:906:27)
at /home/hingo/hacking/impress.js/node_modules/uglify-js/lib/parse-js.js:814:19
at block_ (/home/hingo/hacking/impress.js/node_modules/uglify-js/lib/parse-js.js:1003:20)
You will be pleased to know, that the concatenation of the unminified file
[js/impress.js](../../js/impress.js) has already succeeded at this point. Just
open a test in your browser, and the browser will show you the line and error.
### Structure, naming and policy
Each plugin is contained within its own directory. The name of the directory
is the name of the plugin. For example, imagine a plugin called *pluginA*:
src/plugins/plugina/
The main javascript file should use the directory name as its root name:
src/plugins/plugina/plugina.js
For most plugins, a single `.js` file is enough.
Note that the plugin name is also used as a namespace for various things. For
example, the *autoplay* plugin can be configured by setting the `data-autoplay="5"`
attribute on a `div`.
As a general rule ids, classes and attributes within the `div#impress` root
element, may use the plugin name directly (e.g. `data-autoplay="5"`). However,
outside of the root element, you should use `impress-pluginname` (e.g.
`<div id="impress-toolbar">`. The latter (longer) form also applies to all
events, they should be prefixed with `impress:pluginname`.
You should use crisp and descriptive names for your plugins. But
sometimes you might optimize for a short namespace. Hence, the
[Relative Positioning Plugin](rel/rel.js) is called `rel` to keep html attributes
short. You should not overuse this idea!
Note that for default plugins, which is all plugins in this directory,
**NO css, html or image files** are allowed.
Default plugins must not add any global variables.
### Testing
The plugin directory should also include tests, which should use the *QUnit* and
*Syn* libraries under [test/](../../test). You can have as many tests as you like,
but it is suggested your first and main test file is called `plugina_tests.html`
and `plugina_tests.js` respectively. You need to add your test `.js` file into
[/qunit_test_runner.html](../../qunit_test_runner.html), and the `.js` file
should start by loading the test `.html` file into the
`iframe#presentation-iframe`. See [navigation-ui](navigation-ui) plugin for an
example.
You are allowed to test your plugin whatever way you like, but the general
approach is for the test to load the [js/impress.js](../../js/impress.js) file
produced by build.js. This way you are testing what users will actually be
using, rather than the uncompiled source code.
HowTo write a plugin
--------------------
### Encapsulation
To avoid polluting the global namespace, plugins must encapsulate them in the
standard javascript anonymous function:
/**
* Plugin A - An example plugin
*
* Description...
*
* Copyright 2016 Firstname Lastname, email or github handle
* Released under the MIT license.
*/
(function ( document, window ) {
// Plugin implementation...
})(document, window);
### Init plugins
We categorize plugins into various categories, based on how and when they are
called, and what they do.
An init plugin is the simplest kind of plugin. It simply listens for the
`impress().init()` method to send the `impress:init` event, at which point
the plugin can initialize itself and start doing whatever it does, for example
by calling methods in the public api returned by `impress()`.
Both [Navigation](navigation/navigation.js) and [Autoplay](autoplay/autoplay.js)
are init plugins.
To provide end user configurability in your plugin, a good idea might be to
read html attributes from the impress presentation. The
[Autoplay](autoplay/autoplay.js) plugin does exactly this, you can provide
a default value in the `div#impress` element, or in each `div.step`.
A plugin must only use html attributes in its designated namespace, which is
data-pluginName-*="value"
For example, if *pluginA* offers config options `foo` and `bar`, it would look
like this:
<div id="impress" data-plugina-foo="5" data-plugina-bar="auto" >
### Pre-init plugins
Some plugins need to run before even impress().init() does anything. These
are typically *filters*: they want to modify the html via DOM calls, before
impress.js core parses the presentation. We call these *pre-init plugins*.
A pre-init plugin must be called synchronously, before `impress().init()` is
executed. Plugins can register themselves to be called in the pre-init phase
by calling:
impress.addPreInitPlugin( plugin [, weight] );
The argument `plugin` must be a function. `weight` is optional and defaults to
`10`. Plugins are ordered by weight when they are executed, with lower weight
first.
The [Relative Positioning Plugin](rel/rel.js) is an example of a pre-init plugin.
### Pre-StepLeave plugins
A *pre-stepleave plugin* is called synchronously from impress.js core at the
beginning of `impress().goto()`.
To register a plugin, call
impress.addPreStepLeavePlugin( plugin [, weight] );
When the plugin function is executed, it will be passed an argument
that resembles the `event` object from DOM event handlers:
`event.target` contains the current step, which we are about to leave.
`event.detail.next` contains the element we are about to transition to.
`event.detail.reason` contains a string, one of "next", "prev" or "goto",
which tells you which API function was called to initiate the transition.
`event.detail.transitionDuration` contains the transitionDuration for the
upcoming transition.
A pre-stepleave plugin may alter the values in `event.detail` (except for
`reason`), and this can change the behavior of the upcoming transition.
For example, the `goto` plugin will set the `event.detail.next` to point to
some other element, causing the presentation to jump to that step instead.
### GUI plugins
A *GUI plugin* is actually just an init plugin, but is a special category that
exposes visible widgets or effects in the presentation. For example, it might
provide clickable buttons to go to the next and previous slide.
Note that all plugins shipped in the default set **must not** produce any visible
html elements unless the user asks for it. A recommended best practice is to let
the user add a div element, with an id equaling the plugin's namespace, in the
place where he wants to see whatever visual UI elements the plugin is providing:
<div id="impress-plugina"></div>
Another way to show the elements of a UI plugin might be by allowing the user
to explicitly press a key, like "H" for a help dialog.
[Toolbar plugin](toolbar/README.md) is an example of a GUI plugin. It presents
a toolbar where other plugins can add their buttons in a centralized fashion.
Remember that for default plugins, even GUI plugins, no html files, css files
or images are allowed. Everything must be generated from javascript. The idea
is that users can theme widgets with their own CSS. (A plugin is of course welcome
to provide example CSS that can be copypasted :-)
Dependencies
------------
If *pluginB* depends on the existence of *pluginA*, and also *pluginA* must run
before *pluginB*, then *pluginB* should not listen to the `impress:init` event,
rather *pluginA* should send its own init event, which *pluginB* listens to.
Example:
// pluginA
document.addEventListener("impress:init", function (event) {
// plugin A does it's own initialization first...
// Signal other plugins that plugin A is now initialized
var root = document.querySelector( "div#impress" );
var event = document.createEvent("CustomEvent");
event.initCustomEvent("impress:plugina:init', true, true, { "plugina" : "data..." });
root.dispatchEvent(event);
}, false);
// pluginB
document.addEventListener("impress:init", function (event) {
// plugin B implementation
}, false);
A plugin should use the namespace `impress:pluginname:*` for any events it sends.
In theory all plugins could always send an `init` and other events, but in
practice we're adding them on an as needed basis.

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/**
* Navigation events plugin
*
* As you can see this part is separate from the impress.js core code.
* It's because these navigation actions only need what impress.js provides with
* its simple API.
*
* This plugin is what we call an _init plugin_. It's a simple kind of
* impress.js plugin. When loaded, it starts listening to the `impress:init`
* event. That event listener initializes the plugin functionality - in this
* case we listen to some keypress and mouse events. The only dependencies on
* core impress.js functionality is the `impress:init` method, as well as using
* the public api `next(), prev(),` etc when keys are pressed.
*
* Copyright 2011-2012 Bartek Szopka (@bartaz)
* Released under the MIT license.
* ------------------------------------------------
* author: Bartek Szopka
* version: 0.5.3
* url: http://bartaz.github.com/impress.js/
* source: http://github.com/bartaz/impress.js/
*
*/
/* global document */
( function( document ) {
"use strict";
var triggerEvent = function( el, eventName, detail ) {
var event = document.createEvent( "CustomEvent" );
event.initCustomEvent( eventName, true, true, detail );
el.dispatchEvent( event );
};
// Wait for impress.js to be initialized
document.addEventListener( "impress:init", function( event ) {
// Getting API from event data.
// So you don't event need to know what is the id of the root element
// or anything. `impress:init` event data gives you everything you
// need to control the presentation that was just initialized.
var api = event.detail.api;
// Supported keys are:
// [space] - quite common in presentation software to move forward
// [up] [right] / [down] [left] - again common and natural addition,
// [pgdown] / [pgup] - often triggered by remote controllers,
// [tab] - this one is quite controversial, but the reason it ended up on
// this list is quite an interesting story... Remember that strange part
// in the impress.js code where window is scrolled to 0,0 on every presentation
// step, because sometimes browser scrolls viewport because of the focused element?
// Well, the [tab] key by default navigates around focusable elements, so clicking
// it very often caused scrolling to focused element and breaking impress.js
// positioning. I didn't want to just prevent this default action, so I used [tab]
// as another way to moving to next step... And yes, I know that for the sake of
// consistency I should add [shift+tab] as opposite action...
var isNavigationEvent = function( event ) {
// Don't trigger navigation for example when user returns to browser window with ALT+TAB
if ( event.altKey || event.ctrlKey || event.metaKey ) {
return false;
}
// In the case of TAB, we force step navigation always, overriding the browser
// navigation between input elements, buttons and links.
if ( event.keyCode === 9 ) {
return true;
}
// With the sole exception of TAB, we also ignore keys pressed if shift is down.
if ( event.shiftKey ) {
return false;
}
// For arrows, etc, check that event target is html or body element. This is to allow
// presentations to have, for example, forms with input elements where user can type
// text, including space, and not move to next step.
if ( event.target.nodeName !== "BODY" && event.target.nodeName !== "HTML" ) {
return false;
}
if ( ( event.keyCode >= 32 && event.keyCode <= 34 ) ||
( event.keyCode >= 37 && event.keyCode <= 40 ) ) {
return true;
}
};
// KEYBOARD NAVIGATION HANDLERS
// Prevent default keydown action when one of supported key is pressed.
document.addEventListener( "keydown", function( event ) {
if ( isNavigationEvent( event ) ) {
event.preventDefault();
}
}, false );
// Trigger impress action (next or prev) on keyup.
document.addEventListener( "keyup", function( event ) {
if ( isNavigationEvent( event ) ) {
if ( event.shiftKey ) {
switch ( event.keyCode ) {
case 9: // Shift+tab
api.prev();
break;
}
} else {
switch ( event.keyCode ) {
case 33: // Pg up
case 37: // Left
case 38: // Up
api.prev( event );
break;
case 9: // Tab
case 32: // Space
case 34: // Pg down
case 39: // Right
case 40: // Down
api.next( event );
break;
}
}
event.preventDefault();
}
}, false );
// Delegated handler for clicking on the links to presentation steps
document.addEventListener( "click", function( event ) {
// Event delegation with "bubbling"
// check if event target (or any of its parents is a link)
var target = event.target;
while ( ( target.tagName !== "A" ) &&
( target !== document.documentElement ) ) {
target = target.parentNode;
}
if ( target.tagName === "A" ) {
var href = target.getAttribute( "href" );
// If it's a link to presentation step, target this step
if ( href && href[ 0 ] === "#" ) {
target = document.getElementById( href.slice( 1 ) );
}
}
if ( api.goto( target ) ) {
event.stopImmediatePropagation();
event.preventDefault();
}
}, false );
// Delegated handler for clicking on step elements
document.addEventListener( "click", function( event ) {
var target = event.target;
// Find closest step element that is not active
while ( !( target.classList.contains( "step" ) &&
!target.classList.contains( "active" ) ) &&
( target !== document.documentElement ) ) {
target = target.parentNode;
}
if ( api.goto( target ) ) {
event.preventDefault();
}
}, false );
// Add a line to the help popup
triggerEvent( document, "impress:help:add",
{ command: "Left &amp; Right", text: "Previous &amp; Next step", row: 1 } );
}, false );
} )( document );

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/*
* Copyright 2016 Henrik Ingo (@henrikingo)
*
* Released under the MIT license. See LICENSE file.
*/
/* global QUnit, loadIframe, initPresentation, document, window */
QUnit.module( "Navigation plugin" );
QUnit.test( "Navigation Plugin", function( assert ) {
window.console.log( "Begin navigation plugin" );
var done = assert.async();
loadIframe( "test/core_tests_presentation.html", assert, function() {
initPresentation( assert, function() {
var iframe = document.getElementById( "presentation-iframe" );
var iframeDoc = iframe.contentDocument;
var iframeWin = iframe.contentWindow;
var wait = 5; // Milliseconds
var step1 = iframeDoc.querySelector( "div#step-1" );
var step2 = iframeDoc.querySelector( "div#step-2" );
var step3 = iframeDoc.querySelector( "div#step-3" );
var step4 = iframeDoc.querySelector( "div#fourth" );
var root = iframeDoc.querySelector( "div#impress" );
var i = 0;
var sequence = [ { left: step1,
entered: step2,
next: function() { return iframeWin.syn.type( "bodyid", " " ); },
text: "space (2->3)" },
{ left: step2,
entered: step3,
next: function() { return iframeWin.syn.type( "bodyid", "[right]" ); },
text: "[right] (3->4)" },
{ left: step3,
entered: step4,
next: function() { return iframeWin.syn.type( "bodyid", "\t" ); },
text: "tab (4->1)" },
{ left: step4,
entered: step1,
next: function() { return iframeWin.syn.type( "bodyid", "[down]" ); },
text: "[down] (1->2)" },
{ left: step1,
entered: step2,
next: function() { return iframeWin.syn.type( "bodyid", "[page-down]" ); },
text: "[page-down] (2->3)" },
{ left: step2,
entered: step3,
next: function() { return iframeWin.syn.type( "bodyid", "[page-up]" ); },
text: "[page-up] (3->2)" },
{ left: step3,
entered: step2,
next: function() { return iframeWin.syn.type( "bodyid", "[left]" ); },
text: "[left] (2->1)" },
{ left: step2,
entered: step1,
next: function() { return iframeWin.syn.type( "bodyid", "[up]" ); },
text: "[up] (1->4)" },
{ left: step1,
entered: step4,
next: function() { return iframeWin.syn.click( "step-2", {} ); },
text: "click on 2 (4->2)" },
{ left: step4,
entered: step2,
next: function() { return iframeWin.syn.click( "linktofourth", {} ); },
text: "click on link with href to id=fourth (2->4)" },
{ left: step2,
entered: step4,
next: function() { return iframeWin.impress().goto( 0 ); },
text: "Return to first step with goto(0)." },
{ left: step4,
entered: step1,
next: false }
];
var readyCount = 0;
var readyForNext = function() {
readyCount++;
if ( readyCount % 2 === 0 ) {
if ( sequence[ i ].next ) {
assert.ok( sequence[ i ].next(), sequence[ i ].text );
i++;
} else {
window.console.log( "End navigation plugin" );
done();
}
}
};
// Things to check on impress:stepenter event -----------------------------//
var assertStepEnter = function( event ) {
assert.equal( event.target, sequence[ i ].entered,
event.target.id + " triggered impress:stepenter event." );
readyForNext();
};
var assertStepEnterWrapper = function( event ) {
window.setTimeout( function() { assertStepEnter( event ); }, wait );
};
root.addEventListener( "impress:stepenter", assertStepEnterWrapper );
// Things to check on impress:stepleave event -----------------------------//
var assertStepLeave = function( event ) {
assert.equal( event.target, sequence[ i ].left,
event.target.id + " triggered impress:stepleave event." );
readyForNext();
};
var assertStepLeaveWrapper = function( event ) {
window.setTimeout( function() { assertStepLeave( event ); }, wait );
};
root.addEventListener( "impress:stepleave", assertStepLeaveWrapper );
assert.ok( iframeWin.impress().next(), "next() called and returns ok (1->2)" );
} ); // InitPresentation()
} ); // LoadIframe()
} );
QUnit.test( "Navigation Plugin - No-op tests", function( assert ) {
window.console.log( "Begin navigation no-op" );
var done = assert.async();
loadIframe( "test/core_tests_presentation.html", assert, function() {
initPresentation( assert, function() {
var iframe = document.getElementById( "presentation-iframe" );
var iframeDoc = iframe.contentDocument;
var iframeWin = iframe.contentWindow;
var wait = 5; // Milliseconds
var root = iframeDoc.querySelector( "div#impress" );
// This should never happen -----------------------------//
var assertStepEnter = function( event ) {
assert.ok( false,
event.target.id + " triggered impress:stepenter event." );
};
var assertStepEnterWrapper = function( event ) {
window.setTimeout( function() { assertStepEnter( event ); }, wait );
};
root.addEventListener( "impress:stepenter", assertStepEnterWrapper );
// This should never happen -----------------------------//
var assertStepLeave = function( event ) {
assert.ok( false,
event.target.id + " triggered impress:stepleave event." );
};
var assertStepLeaveWrapper = function( event ) {
window.setTimeout( function() { assertStepLeave( event ); }, wait );
};
root.addEventListener( "impress:stepleave", assertStepLeaveWrapper );
// These are no-op actions, we're already in step-1 -----------------------//
assert.ok( iframeWin.syn.click( "step-1", {} ),
"Click on step that is currently active, should do nothing." );
assert.ok( iframeWin.syn.click( "linktofirst", {} ),
"Click on link pointing to step that is currently active, should do nothing." );
// After delay, if no event triggers are called. We're done.
window.setTimeout( function() {
window.console.log( "End navigation no-op" ); done();
}, 3000 );
} ); // InitPresentation()
} ); // LoadIframe()
} );

47
src/plugins/resize/resize.js Normal file
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@@ -0,0 +1,47 @@
/**
* Resize plugin
*
* Rescale the presentation after a window resize.
*
* Copyright 2011-2012 Bartek Szopka (@bartaz)
* Released under the MIT license.
* ------------------------------------------------
* author: Bartek Szopka
* version: 0.5.3
* url: http://bartaz.github.com/impress.js/
* source: http://github.com/bartaz/impress.js/
*
*/
/* global document, window */
( function( document, window ) {
"use strict";
// Throttling function calls, by Remy Sharp
// http://remysharp.com/2010/07/21/throttling-function-calls/
var throttle = function( fn, delay ) {
var timer = null;
return function() {
var context = this, args = arguments;
window.clearTimeout( timer );
timer = window.setTimeout( function() {
fn.apply( context, args );
}, delay );
};
};
// Wait for impress.js to be initialized
document.addEventListener( "impress:init", function( event ) {
var api = event.detail.api;
// Rescale presentation when window is resized
window.addEventListener( "resize", throttle( function() {
// Force going to active step again, to trigger rescaling
api.goto( document.querySelector( ".step.active" ), 500 );
}, 250 ), false );
}, false );
} )( document, window );