` element to become visible. Extra addons ------------ Yet more features are available in presentations that enable [extra addons](https://github.com/impress/impress-extras). Extra addons are 3rd party plugins that are not part of impress.js, but that we have nevertheless collected together into the impress-extras repo to provide convenient and standardized access to them. To include the extra addons when checking out impress.js, use git clone --recursive. Even then, they are not activated by default in a presentation, rather each must be included with their own ` ### 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. `

`. 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()`. The `impress:init` event has the `div#impress` element as its `target` attribute, whereas `event.detail.api` contains the same object that is returned by calling `impress()`. It is customary to store the api object sent by the event rather than calling `impress()` from the global namespace. Example: /** * Plugin A - An example plugin * * Description... * * Copyright 2016 Firstname Lastname, email or github handle * Released under the MIT license. */ (function ( document, window ) { var root; var api; var lib; document.addEventListener( "impress:init", function( event ) { root = event.target; api = event.detail.api; lib = api.lib; // Element attributes starting with "data-", become available under // element.dataset. In addition hyphenized words become camelCased. var data = root.dataset; // Get value of `

` var foo = data.pluginaFoo; // ... } })(document, window); 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:

### 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:

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.