Server-Sent Events (SSE) is a server push technology enabling a client to receive automatic updates from a server via an HTTP connection, and describes how servers can initiate data transmission towards clients once an initial client connection has been established. They are commonly used to send message updates or continuous data streams to a browser client and designed to enhance native, cross-browser streaming through a JavaScript API called EventSource, through which a client requests a particular URL in order to receive an event stream. The EventSource API is standardized as part of HTML5 [1] by the WHATWG. The media type for SSE is text/event-stream.
All modern browsers support server-sent events: Firefox 6+, Google Chrome 6+, Opera 11.5+, Safari 5+, Microsoft Edge 79+. [2]
The SSE mechanism was first specified by Ian Hickson as part of the "WHATWG Web Applications 1.0" proposal starting in 2004. [3] In September 2006, the Opera web browser implemented the experimental technology in a feature called "Server-Sent Events". [4] [5]
The Document Object Model (DOM) is a cross-platform and language-independent interface that treats an HTML or XML document as a tree structure wherein each node is an object representing a part of the document. The DOM represents a document with a logical tree. Each branch of the tree ends in a node, and each node contains objects. DOM methods allow programmatic access to the tree; with them one can change the structure, style or content of a document. Nodes can have event handlers attached to them. Once an event is triggered, the event handlers get executed.
XMLHttpRequest (XHR) is a JavaScript class containing methods to asynchronously transmit HTTP requests from a web browser to a web server. The methods allow a browser-based application to make a fine-grained server call and store the results in XMLHttpRequest's responseText attribute. The XMLHttpRequest class is a component of Ajax programming. Prior to Ajax, an HTML form needed to be completely sent to the server followed by a complete browser page refresh.
Push technology, also known as server push, refers to a method of communication on the Internet where the initial request for a transaction is initiated by the server, rather than the client. This approach is different from the more commonly known "pull" method, where information transmission is requested by the receiver or client.
The canvas element is part of HTML5 and allows for dynamic, scriptable rendering of 2D shapes and bitmap images. It is a low level, procedural model that updates a bitmap. HTML5 Canvas also helps in making 2D games.
Comet is a web application model in which a long-held HTTPS request allows a web server to push data to a browser, without the browser explicitly requesting it. Comet is an umbrella term, encompassing multiple techniques for achieving this interaction. All these methods rely on features included by default in browsers, such as JavaScript, rather than on non-default plugins. The Comet approach differs from the original model of the web, in which a browser requests a complete web page at a time.
HTML5 is a markup language used for structuring and presenting hypertext documents on the World Wide Web. It was the fifth and final major HTML version that is now a retired World Wide Web Consortium (W3C) recommendation. The current specification is known as the HTML Living Standard. It is maintained by the Web Hypertext Application Technology Working Group (WHATWG), a consortium of the major browser vendors.
The Web Hypertext Application Technology Working Group (WHATWG) is a community of people interested in evolving HTML and related technologies. The WHATWG was founded by individuals from Apple Inc., the Mozilla Foundation and Opera Software, leading Web browser vendors in 2004.
A single-page application (SPA) is a web application or website that interacts with the user by dynamically rewriting the current web page with new data from the web server, instead of the default method of a web browser loading entire new pages. The goal is faster transitions that make the website feel more like a native app.
Extensible HyperText Markup Language (XHTML) is part of the family of XML markup languages which mirrors or extends versions of the widely used HyperText Markup Language (HTML), the language in which Web pages are formulated.
Web storage, sometimes known as DOM storage, is a standard JavaScript API provided by web browsers. It enables websites to store persistent data on users' devices similar to cookies, but with much larger capacity and no information sent in HTTP headers. There are two main web storage types: local storage and session storage, behaving similarly to persistent cookies and session cookies respectively. Web Storage is standardized by the World Wide Web Consortium (W3C) and WHATWG, and is supported by all major browsers.
WebSocket is a computer communications protocol, providing simultaneous two-way communication channels over a single Transmission Control Protocol (TCP) connection. The WebSocket protocol was standardized by the IETF as RFC 6455 in 2011. The current specification allowing web applications to use this protocol is known as WebSockets. It is a living standard maintained by the WHATWG and a successor to The WebSocket API from the W3C.
Microdata is a WHATWG HTML specification used to nest metadata within existing content on web pages. Search engines, web crawlers, and browsers can extract and process Microdata from a web page and use it to provide a richer browsing experience for users. Search engines benefit greatly from direct access to Microdata because it allows them to understand the information on web pages and provide more relevant results to users. Microdata uses a supporting vocabulary to describe an item and name-value pairs to assign values to its properties. Microdata is an attempt to provide a simpler way of annotating HTML elements with machine-readable tags than the similar approaches of using RDFa and microformats.
The HTML5 specification introduced the video element for the purpose of playing videos, partially replacing the object element. HTML5 video is intended by its creators to become the new standard way to show video on the web, instead of the previous de facto standard of using the proprietary Adobe Flash plugin, though early adoption was hampered by lack of agreement as to which video coding formats and audio coding formats should be supported in web browsers. As of 2020, HTML5 video is the only widely supported video playback technology in modern browsers, with the Flash plugin being phased out.
Web Messaging, or cross-document messaging, is an API introduced in the WHATWG HTML5 draft specification, allowing documents to communicate with one another across different origins, or source domains while rendered in a web browser. Prior to HTML5, web browsers disallowed cross-site scripting, to protect against security attacks. This practice barred communication between non-hostile pages as well, making document interaction of any kind difficult. Cross-document messaging allows scripts to interact across these boundaries, while providing a rudimentary level of security.
WebRTC is a free and open-source project providing web browsers and mobile applications with real-time communication (RTC) via application programming interfaces (APIs). It allows audio and video communication to work inside web pages by allowing direct peer-to-peer communication, eliminating the need to install plugins or download native apps.
Content Security Policy (CSP) is a computer security standard introduced to prevent cross-site scripting (XSS), clickjacking and other code injection attacks resulting from execution of malicious content in the trusted web page context. It is a Candidate Recommendation of the W3C working group on Web Application Security, widely supported by modern web browsers. CSP provides a standard method for website owners to declare approved origins of content that browsers should be allowed to load on that website—covered types are JavaScript, CSS, HTML frames, web workers, fonts, images, embeddable objects such as Java applets, ActiveX, audio and video files, and other HTML5 features.
HTML5 Audio is a subject of the HTML5 specification, incorporating audio input, playback, and synthesis, as well as in the browser. iOS
SignalR is a free and open-source software library for Microsoft ASP.NET that allows server code to send asynchronous notifications to client-side web applications. The library includes server-side and client-side JavaScript components.
Media Source Extensions (MSE) is a W3C specification that allows JavaScript to send byte streams to media codecs within web browsers that support HTML5 video and audio. Among other possible uses, this allows the implementation of client-side prefetching and buffering code for streaming media entirely in JavaScript. It is compatible with, but should not be confused with, the Encrypted Media Extensions (EME) specification, and neither requires the use of the other, although many EME implementations are only capable of decrypting media data provided via MSE.
Anne van Kesteren is an open web standards author and open source contributor. He has written and edits several web standards specifications including Fullscreen API, XMLHttpRequest, and URL. Formerly worked on standards issues as a software engineer at Opera Software, he started working at Mozilla on 2013-02-04. He was Mozilla’s representative on the WHATWG Steering Group. He was an elected participant in the W3C Technical Architecture Group (TAG) from 2013 to 2014.
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