Web Components

Web Components are a set of features currently being added by the W3C to the HTML and DOM specifications that allow for the creation of reusable widgets or components in web documents and web applications.

The intention behind them is to bring component-based software engineering to the World Wide Web. The components model allows for encapsulation and interoperability of individual HTML elements - wikipedia

There are two parts to Custom Elements: autonomous custom elements and customized built-in elements.

Autonomous custom elements are HTML elements that are entirely separated from native HTML elements, they are essentially built from the bottom up using the Custom Elements API (Application programming interface).

Customized built-in elements are elements that are built upon native HTML elements to reuse their functionality.Custom Elements

Shadow DOM is a functionality that allows the web browser to render DOM elements without putting them into the main document DOM tree.

This creates a barrier between what the developer and the browser can reach; the developer cannot access the Shadow DOM in the same way they would with nested elements, while the browser can render and modify that code the same way it would with nested elements.

The impact of CSS scoped within the Shadow DOM of a particular element is that HTML elements can be encapsulated without the risk of CSS (Cascading Style Sheets) styles leaking and affecting elements that it was not supposed to affect.

Although these elements are encapsulated with regard to HTML and CSS, they can still fire events that can be picked up by other elements in the document - glazkov.com

The ability to scope HTML and CSS (Cascading Style Sheets) is essential to the creation of Custom Elements. If shadow DOM did not exist, different external Custom Elements could interact in unwanted ways.

HTML import is a tool to include HTML documents and web components from external sources without using AJAX (Ajax (programming)) requests and similar methods - w3.org

The syntax for doing an HTML import looks like this:

Mozilla Firefox (Firefox) has no support for HTML import and does not intend to implement it - mozilla.org

HTML Import is also related to an early idea in the development of hypertext called Transclusion, where all or part of an document is inserted into another by reference.

HTML template is a way to create insert chunks of HTML that are stamped at will. The syntax of HTML templates look like this:

There are several libraries that are built on Web Components with the aim of increasing the level of abstraction when creating custom elements. Four of the familiar libraries are X-Tag , Slim.js, Polymer (Polymer (library)), and Bosonic.

Two of these, Bosonic and Polymer, provide ready-made components that are free to use. These components can be used interchangeably as they are all built on open web technologies - vaadin.com