2 December 2005 Web Technologies HTML5 and the Open Web Platform Prof. Beat Signer Department of Computer Science Vrije Universiteit Brussel beatsigner.com
Beat Signer - Department of Computer Science - [email protected] 2 October 11, 2022 Hypertext Markup Language (HTML) ▪ HTML is an application of the Standard Generalized Markup Language (SGML) ▪ simple human-readable markup language with a number of markup tags that can be manipulated by any text editor ▪ Various markup tags to define the structure and presentation of a HTML document (webpage) ▪ root element (), header (), body () and title () ▪ headings (, ... ) and paragraphs () ▪ tables (, and ) and lists (, and ) ▪ images () ▪ w3schools provides a detailed list of tags ▪ https://www.w3schools.com/tags/
Beat Signer - Department of Computer Science - [email protected] 3 October 11, 2022 Hypertext Markup Language (HTML) ... ▪ Tags can be nested and attributes (key/value pairs) can be added to a tag ▪ HTML documents are transformed into a Document Object Model (DOM) by the browser ▪ tree of elements (and attributes) with textual content ▪ HTML DOM defines objects and properties for HTML elements - document node, element nodes, text nodes, attribute nodes and comment nodes ▪ standard to create, read, update and delete HTML elements ▪ Hyperlinks to connect different HTML documents ▪ only unidirectional embedded hyperlinks are supported
Beat Signer - Department of Computer Science - [email protected] 4 October 11, 2022 HTML Example PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
Vrije Universiteit Brussel
News Internationalisation was this year's theme of the academic opening of the Vrije Universiteit Brussel.
The Vrije Universiteit Brussel will organise the new International Business Arbitration post-graduate course from the new academic year onwards.
Beat Signer - Department of Computer Science - [email protected] 5 October 11, 2022 HTML DOM Example News html head body document title Vrije Univer ... h1 p p … … a Internationa ... Vrije Uni ... href https:// ... document node element node attribute node text node root node
Beat Signer - Department of Computer Science - [email protected] 6 October 11, 2022 History of HTML ▪ HTML 1.0 (1993), prototype already in 1991 ▪ HTML 2.0 (1995) ▪ at that time the Netscape Navigator offered much more functionality than the HTML standard - "browser war" between Netscape and Internet Explorer ▪ HTML 3.2 (1997) ▪ first version that was developed exclusively by the Word Wide Web Consortium (W3C) ▪ introduced tables ▪ introduced a lot of new elements for the visual appearance of a document (that was not the original idea of HTML!) - e.g. element or color attribute - most elements now deprecated and cascading style sheets should be used
Beat Signer - Department of Computer Science - [email protected] 7 October 11, 2022 History of HTML ... ▪ HTML 4.0 (1997) and HTML 4.01 (1999) ▪ internationalisation (Unicode) ▪ introduction of Cascading Style Sheets (CSS) ▪ In 1998 the W3C decided to not further evolve HTML! ▪ XHTML 1 (2000) and XHTML 1.1 (2001) ▪ XML version of HTML (draconian error handling) ▪ XHTML 2.0 (never finished, discontinued in 2009) ▪ revolutionary changes → breaking backwards compatibility ▪ Web Hypertext Application Technology Working Group (WHATWG) founded in 2004 (led by Ian Hickson) ▪ Web Forms 2.0 and Web Applications 1.0 → HTML5
Beat Signer - Department of Computer Science - [email protected] 8 October 11, 2022 History of HTML ... ▪ In 2006 the W3C decided to work on HTML again ▪ based on WHATWG's Web Applications specification ▪ HTML5 specification was developed simultaneously by the WHATWG and the W3C until 2019 ▪ HTML - Living Standard, WHATWG ▪ HTML5 - A Vocabulary and Associated APIs for HTML and XHTML ▪ Since 2019 HTML - Living Standard is the only standard ▪ developed by WHATWG and W3C
Beat Signer - Department of Computer Science - [email protected] 9 October 11, 2022 Problems with HTML ▪ Mix of content, structure and presentation ▪ no separation of concerns ▪ structure of content defines the presentation in the browser ▪ "Forgiving" browsers weaken the standard ▪ an HTML document with errors (e.g. missing tags etc.) will still be rendered without any error messages ▪ HTML documents can be checked against the standard - https://validator.w3.org ▪ most existing websites (>99%) contain errors - exercise: can you find a webpage without any errors?
Beat Signer - Department of Computer Science - [email protected] 10 October 11, 2022 XHTML ▪ XHTML is a reformulation of HTML to make it an XML application (instead of SGML) ▪ we accept that HTML is here to stay ▪ improve HTML by using XML (e.g. nesting or closing of tags) ▪ use benefits of XML with minimal effort "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
Beat Signer - Department of Computer Science - [email protected] 11 October 11, 2022 HTML5 ... HTML5 does not belong to a company or a specific browser. It has been forged by a community of people interested in evolving the web and a consortium of technological leaders that includes Google, Microsoft, Apple, Mozilla, Facebook, IBM, HP, Adobe, and many others. The community and consortium continue to collaborate on universal browser standards to push web capabilities even further. The next generation of web apps can run high- performance graphics, work offline, store a large amount of data on the client, perform calculations fast, and take interactivity and collaboration to the next level. ... Why HTML5 Rocks, http://www.html5rocks.com
Beat Signer - Department of Computer Science - [email protected] 12 October 11, 2022 HTML5 Design Principles ▪ Compatibility ▪ evolve the language (backward compatibility) ▪ Utility ▪ solve real problems (pragmatic approach) ▪ separation of content and presentation (CSS) ▪ Interoperability ▪ interoperable browser behaviour ▪ identical error handling across browsers resulting in the same DOM tree for broken HTML ▪ Universal Access ▪ features should preferably work across different platforms (cross-platform), devices and media ▪ design features should be accessible to users with disabilities
Beat Signer - Department of Computer Science - [email protected] 13 October 11, 2022 HTML5 Design Principles ... ▪ Simple is better ▪ new doctype: ▪ HTML5 APIs ▪ ... ▪ Avoid external plug-ins ▪ plug-ins are often not nicely integrated with HTML documents ▪ plug-ins can be disabled or blocked (e.g. Adobe Flash on iPad) ▪ plug-ins might crash ▪ ...
Beat Signer - Department of Computer Science - [email protected] 14 October 11, 2022 HTML5 and Open Web Platform APIs W3C Recommendation W3C Candidate Recommendation Working Draft W3C Working Group Note Non-W3C Specification HTML Markup Canvas 2D Web Messaging Audio Video Web Sockets Drag and Drop Web Workers Micro data Web Storage HTML+ RDFa XmlHTTP Request File API Media Capure Indexed Database Contacts API Screen Orientation Timing Control Touch Events Geo Location RDFa Web Open Font Navigation Timing Selectors L1 SVG MathML 3.0 CSS3 Battery Status API Fullscreen JavaScript WebGL based on https://en.wikipedia.org/wiki/HTML5#/ ▪ Simplifies implementation of cross-platform applications ▪ Standard way for accessing specific functionality ▪ No need for plug-in installation
Beat Signer - Department of Computer Science - [email protected] 15 October 11, 2022 JavaScript/ECMAScript ▪ Growing use of JavaScript frameworks and AJAX ▪ JavaScript engine race ▪ in 2006 Adobe donated their just-in-time (JIT) compilation engine and ECMAScript virtual machine to the Mozilla project ▪ healthy competition among browser vendors - bring JavaScript performance closer to that of native desktop application code https://www.devsaran.com/blog/10-best-programming-languages-2020-you-should-know Most Popular Programming Languages of 2020
Beat Signer - Department of Computer Science - [email protected] 17 October 11, 2022 Web Browsers (1990–2022) https://en.wikipedia.org/wiki/File:Timeline_of_web_browsers.svg Internet Explorer Mozilla Gecko Engine Trident Engine Firefox WebKit Engine Safari Chrome
Beat Signer - Department of Computer Science - [email protected] 18 October 11, 2022 HTML Markup ▪ Some elements have been added ▪ structural elements such as , , , or ▪ media elements including , or ▪ a drawing element ▪ Other elements have been removed ▪ , , , , , ... ▪ New form functionality (originally Web Forms 2.0) ▪ form elements such as or ▪ input types such as date, color, email, tel, range, ... ▪ native functionality for client-side validation (without scripting) W3C Recommendation
Beat Signer - Department of Computer Science - [email protected] 22 October 11, 2022 HTML Forms ... ▪ Filled in information is sent to the server as name/value pairs in an HTTP GET or HTTP POST request ▪ HTML5 forms simplify the client-side validation of input fields ▪ validation based on input type and other optional attributes ▪ valid input for text input fields can be defined via the pattern attribute (regular expression) ▪ no longer necessary to use JavaScript for client-side validation
Beat Signer - Department of Computer Science - [email protected] 23 October 11, 2022 HTML Links ▪ Only unidirectional embedded links are supported ▪ Linking to parts of another document ▪ only possible if we can add id attributes
...
VUB VUB Contact us Email John Introduction page (identified via an id attribute with the corresponding name) -->
Beat Signer - Department of Computer Science - [email protected] 24 October 11, 2022 Video ▪ element can be used to play videos in HTML pages ▪ element has methods, properties and events ▪ no external plug-in (e.g. Adobe Flash) required anymore ▪ e.g. in early 2015 YouTube switched from Flash to HTML5 video as the default ▪ Multiple video formats are supported ▪ MP4, WebM and Ogg
Beat Signer - Department of Computer Science - [email protected] 25 October 11, 2022 Audio ▪ element can be used to play audio in HTML pages ▪ element has methods, properties and events
Beat Signer - Department of Computer Science - [email protected] 26 October 11, 2022 Canvas 2D ▪ tag can be used in combination with JavaScript to draw on a webpage (raster graphics) ▪ define a canvas with an id and use it in the JavaScript code ▪ draw lines, shapes (with optional gradient filling) etc. or add text
Beat Signer - Department of Computer Science - [email protected] 28 October 11, 2022 Scalable Vector Graphics (SVG) ▪ Vector graphics alternative to Canvas 2D ▪ resolution independent ▪ define graphics in XML format (embeddable in HTML) ▪ good support for animations (declarative description) ▪ full control over each element via the SVG DOM API ▪ On the other hand, Canvas 2D offers better performance W3C Recommendation
Beat Signer - Department of Computer Science - [email protected] 29 October 11, 2022 Web Graphics Library (WebGL) ▪ 3D graphics API for JavaScript ▪ getContext("3d") might be used in the future ▪ currently getContext("webgl") or getContext("webgl2") ▪ GPU accelerated
Beat Signer - Department of Computer Science - [email protected] 31 October 11, 2022 Web Storage API ▪ localStorage and sessionStorage JavaScript objects to store data (key/value) on the client ▪ localStorage has no time limit whereas sessionStorage is deleted when the browser window is closed - localStorage with same-origin policy and sessionStorage per window ▪ replace cookies for large amounts of data - cookies are limited in size (maximal 4 kB) and are sent with each request W3C Recommendation <br/>if (localStorage.counter) {<br/>localStorage.counter = Number(localStorage.counter) + 1;<br/>}<br/>else {<br/>localStorage.counter = 1;<br/>}<br/>document.write("Total of " + localStorage.counter + " visits");<br/>
Beat Signer - Department of Computer Science - [email protected] 32 October 11, 2022 Drag and Drop ▪ Drag items and drop them anywhere in the browser ▪ define draggable elements via the draggable attribute ▪ define elements that can accept drops ▪ exchange information via the dataTransfer object ▪ Items can also be drag and dropped from the desktop to the browser W3C Recommendation
Beat Signer - Department of Computer Science - [email protected] 33 October 11, 2022 Drag and Drop ...
// style sheet information for the div elements <br/>function drag(event) {<br/>event.dataTransfer.setData("text/plain", event.target.id);<br/>}<br/>function drop(event) {<br/>event.preventDefault(); // avoid default behaviour of opening as link<br/>var data=event.dataTransfer.getData("text/plain");<br/>event.target.appendChild(document.getElementById(data));<br/>}<br/>function allowDrop(event) {<br/>event.preventDefault();<br/>}<br/>
Beat Signer - Department of Computer Science - [email protected] 35 October 11, 2022 Web Workers ▪ When executing JavaScript in an HTML page, the page becomes non-responsive until the script is finished ▪ Web Workers can be used to execute JavaScript code in a background process (thread) ▪ to avoid the complexity of multi-threaded programming, Web Workers have independent JavaScript contexts and can only interact with each other via event-driven message passing W3C Working Draft <br/>var worker = new Worker("myScript.js");<br/>worker.onmessage = function(event) {<br/>alert("The worker received this: " + event.data);<br/>// web worker sends a message back<br/>postMessage("I got your call and will work on it");<br/>...<br/>};<br/>
Beat Signer - Department of Computer Science - [email protected] 36 October 11, 2022 Web Workers ... ▪ Note that Web Workers have no access to window.document (web page or DOM API) ▪ "clean up" Web Workers via terminate() method // add a listener to receive messages from the web worker worker.addEventListener("message", handle, false); function handle(e) { // process message from the web worker } worker.postMessage("Hello worker!");
Beat Signer - Department of Computer Science - [email protected] 37 October 11, 2022 WebSocket API ▪ Bidirectional, full-duplex socket connection between the server and browser for real-time web applications (low latency) with asynchronous partial updates ▪ server-initiated updates become possible! ▪ client and server upgrade from the HTTP protocol to the WebSocket protocol (initial HTTP handshake) - via Connection: Upgrade and Upgrade: websocket HTTP header fields - browser as well as server have to support the Web Socket protocol ▪ reduced "overhead" since no HTTP headers ▪ no longer necessary to do any polling or long polling - faster since in the polling approach the server can send nothing while a client request is transmitted ▪ similarly an EventSource object can be used if only the server has to push information (server-sent events) W3C Candidate Recommendation
Beat Signer - Department of Computer Science - [email protected] 39 October 11, 2022 Geolocation API ▪ Standard interface for accessing geographical location information on the client device ▪ transparent access to different location information sources - GPS, GSM cells, IP address, RFID, Wi-Fi connection etc. ▪ Firefox uses the Google Location Service as default lookup service ▪ send IP address and information about nearby wireless access points to the Google Location Service and an approximate location will be computed W3C Recommendation
Beat Signer - Department of Computer Science - [email protected] 40 October 11, 2022 Geolocation API ... ▪ JavaScript access to the Geolocation API ▪ access via the geolocation child object of the navigator object ▪ we can also continuously monitor the client's position function showPosition(position) { alert(position.coords.latitude + " " + position.coords.longitude); } function showError() { alert("Your current position cannot be computed!"); } navigator.geolocation.getCurrentPosition(showPosition, showError, {timeout:10000}); navigator.geolocation.watchPosition(showPosition); W3C Recommendation
Beat Signer - Department of Computer Science - [email protected] 42 October 11, 2022 Offline Web Applications ▪ Application cache is used for ▪ offline browsing where users can use the web application while they are offline ▪ increased performance due to cache hits and reduced server load ▪ Managed via a cache manifest (on every page) W3C Working Group Note
Beat Signer - Department of Computer Science - [email protected] 43 October 11, 2022 Fullscreen API ▪ Can be used to show elements in fullscreen mode ▪ requestFullscreen() and exitFullScreen() W3C Working Group Note
var video = document.getElementById("video1"); if (video.requestFullscreen) { // different browser implementations video.requestFullscreen(); } else if (video.msRequestFullscreen) { // IE11 video.msRequestFullscreen(); } else if (video.webkitRequestFullscreen) { // Safari video.webkitRequestFullscreen(); }
Beat Signer - Department of Computer Science - [email protected] 44 October 11, 2022 Screen Orientation API ▪ Provides access to the orientation of the screen ▪ portrait-primary, portrait-secondary, landscape-primary or landscape-secondary W3C Working Draft // add a listener to react to changes of screen orientation screen.orientation.addEventListener("change", function () { console.log("The orientation of the screen is: " + screen.orientation); }); // lock the screen in portrait or landscape orientation screen.orientation.lock("landscape"); // unlock the screen screen.orientation.unlock();
Beat Signer - Department of Computer Science - [email protected] 45 October 11, 2022 Page Visibility API ▪ Provides information about the current visibility of a page ▪ we can adapt behaviour if a page is not visible (e.g. minimised) - change update frequency (e.g. checking for emails) to save resources - pause video or game - do not charge for ads W3C Recommendation var video = document.getElementById("video1"); // assume we have a video document.addEventListener("visibilitychange", handle, false); function handle() { if (document.hidden) { video.pause(); } else { video.play(); } }
Beat Signer - Department of Computer Science - [email protected] 46 October 11, 2022 Battery Status API ▪ Provides Information about the battery status of the hosting device ▪ e.g. to reduce battery drain when the battery is low W3C Candidate Recommendation var battery = navigator.battery; console.log("Battery level: " + Math.floor(battery.level * 100) + "%"); console.log("Device is " + (battery.charging ? "charging" : "discharging"); console.log("Battery charged in " + battery.chargingTime + "s"); console.log("Battery empty in " + battery.dischargingTime + "s"); // we can further register to the following events: chargingchange, levelchange, chargingtimechange and dischargingtimechange battery.onlevelchange = function() { ... }
Beat Signer - Department of Computer Science - [email protected] 47 October 11, 2022 Vibration API ▪ Provide simple tactile feedback ▪ simple vibration or pattern of on/off pulses ▪ feedback for mobile phones and other devices ▪ for devices not supporting vibrations, the methods have no effect W3C Recommendation // single vibration for 300ms navigator.vibrate(300); // pattern with pauses of 50ms navigator.vibrate([300, 50, 300, 50, 1000]); // ongoing vibrations can be cancelled at any time by calling the vibrate method with a value of zero navigator.vibrate(0);
Beat Signer - Department of Computer Science - [email protected] 48 October 11, 2022 Web Notifications API ▪ Display notifications to alert users outside the context of a web page ▪ show standard desktop notifications (e.g. lower right corner) W3C Recommendation Notification.requestPermission(); // ask for permission var options = { body: "This is the body of my message", icon: "data:image/png;base64,iVBORw0KGgoAAAANSUhE" }; var notification = new Notification("My Title", options);
Beat Signer - Department of Computer Science - [email protected] 49 October 11, 2022 Example: Multiplayer Port of Quake II ▪ Google's browser port of Quake II uses ▪ canvas and WebGL ▪ for sound ▪ for in-game videos ▪ Web Sockets for communication with the server (other players) ▪ Local Storage for managing preferences and saved games
Beat Signer - Department of Computer Science - [email protected] 50 October 11, 2022 Other HTML5 Features ▪ Media Capture and Streams ▪ access local multimedia devices such as microphones or video cameras ▪ Web Messaging ▪ communication between documents (e.g. in different frames, tabs or windows) regardless of their source domain ▪ messages should only be accepted from domains we expect to receive messages from ▪ WebRTC 1.0: Real-time Communication Between Browsers ▪ real-time browser-to-browser applications for voice calling, video chat etc.
Beat Signer - Department of Computer Science - [email protected] 51 October 11, 2022 Other HTML5 Features … ▪ Note that some other HTML5 features are introduced later in the course ▪ Microdata ▪ …
Beat Signer - Department of Computer Science - [email protected] 53 October 11, 2022 References ▪ Mark Pilgrim, HTML5: Up and Running – Dive Into the Future of Web Development, O'Reilly Media, August 2010 ISBN-13: 978-0596806026 ▪ HTML - Living Standard ▪ https://html.spec.whatwg.org/multipage/ ▪ HTML Design Principles, W3C Working Draft ▪ https://www.w3.org/TR/html-design-principles/ ▪ HTML Tutorial ▪ https://www.w3schools.com/html/
Beat Signer - Department of Computer Science - [email protected] 54 October 11, 2022 References ... ▪ Simon Sarris, HTML 5 Canvas: A Web Standard for Dynamic Graphics (refcardz #151) ▪ https://dzone.com/refcardz/html5-canvas-web-standard ▪ HTML5 Canvas and JavaScript Demo ▪ http://www.youtube.com/watch?v=cnexWE5Rbx4 ▪ Scalable Vector Graphics (SVG) 2, W3C Recommendation ▪ https://www.w3.org/TR/SVG2/ ▪ Andy Harris, Core HTML (refcardz #64) ▪ https://dzone.com/refcardz/core-html
Beat Signer - Department of Computer Science - [email protected] 55 October 11, 2022 References ... ▪ James Sugrue, HTML5: The Evolution of Web Standards (refcardz #123) ▪ https://dzone.com/refcardz/html5-new-standards-web-interactivity ▪ Offline Web Applications, W3C Working Group Note ▪ https://www.w3.org/TR/offline-webapps/ ▪ Max Firtman, HTML5 Mobile Development, (refcardz #186) ▪ https://dzone.com/refcardz/html5-mobile-development ▪ W3C Markup Validation Service ▪ https://validator.w3.org
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