This core language is also used in non-browser environments, for example in node.js.
What falls under the ECMAScript scope?
Among other things, ECMAScript defines:
- Language syntax (parsing rules, keywords, control flow, object literal initialization, ...)
- Error handling mechanisms (throw, try/catch, ability to create user-defined Error types)
- Types (boolean, number, string, function, object, ...)
- The global object. In a browser, this global object is the window object, but ECMAScript only defines the APIs not specific to browsers, e.g.
- A prototype-based inheritance mechanism of:
- Built-in objects and functions (
Array.prototypemethods, Object introspection methods, etc.)
- Strict mode (see here)
The major 6th Edition of ECMAScript was officially approved and published as a standard on June 17, 2015 by the ECMA General Assembly. Since then ECMAScript Editions are published on a yearly basis.
Intl object. The Internationalization specification is nowadays also ratified on a yearly basis and browsers constantly improve their implementation.
The WebIDL specification provides the glue between the DOM technologies and ECMAScript.
The Core of the DOM
The Document Object Model (DOM) is a cross-platform, language-independent convention for representing and interacting with objects in HTML, XHTML and XML documents. Objects in the DOM tree may be addressed and manipulated by using methods on the objects. The W3C standardizes the Core Document Object Model, which defines language-agnostic interfaces that abstract HTML and XML documents as objects, and also defines mechanisms to manipulate this abstraction. Among the things defined by the DOM, we can find:
- The document structure, a tree model, and the DOM Event architecture in DOM core:
- A less rigorous definition of the DOM Event Architecture, as well as specific events in DOM events.
- Other things such as DOM Traversal and DOM Range.
From the ECMAScript point of view, objects defined in the DOM specification are called "host objects".
HTML, the Web's markup language, is specified in terms of the DOM. Layered above the abstract concepts defined in DOM Core, HTML also defines the meaning of elements. The HTML DOM includes such things as the
className property on HTML elements, or APIs such as
The HTML specification also defines restrictions on documents; for example, it requires all children of a
ul element, which represents an unordered list, to be
li elements, as those represent list items. In general, it also forbids using elements and attributes that aren't defined in a standard.
Other notable APIs
setIntervalfunctions were first specified on the
Windowinterface in HTML Standard.
- XMLHttpRequest makes it possible to send asynchronous HTTP requests.
- The CSS Object Model abstract CSS rules as objects.
- WebWorkers allows parallel computation.
- WebSockets allows low-level bidirectional communication.
- Canvas 2D Context is a drawing API for
As every web developer has experienced, the DOM is a mess. Browser support uniformity varies a lot from feature to feature, mainly because many important DOM features have very unclear specifications (if any), and different web browsers add incompatible features for overlapping use cases (like the Internet Explorer event model). As of June 2011, the W3C and particularly the WHATWG are defining older features in detail to improve interoperability, and browsers in turn can improve their implementations based on these specifications.