HTML Components

Using custom elements A guide showing how to use the features of custom elements to create simple web components, as well as looking into lifecycle callbacks and some other more advanced features. If required, attach a shadow DOM to the custom element using Element.attachShadow() method.

• A string representing the name you are giving to the element.
• ShadowRoot Represents the root node of a shadow DOM subtree.
• Some of the examples in this document use a linking mechanism based on CSS stylesheets that has not been approved by the W3C.
• It brings a web standards-based way to create reusable components using nothing more than vanilla JS/HTML/CSS.
• You can’t rely on your element being removed from the DOM in all circumstances.
• The above two components are equivalent from React’s point of view.

In this article, I’ll discuss why Web Components are a great tool to deliver high-quality user experiences without complicated frameworks or build steps and that don’t run the risk of becoming obsolete. In subsequent articles of this five-part series, we will dive deeper into each of the specifications.

Character Sets

If you’ve ever written a component that reuses the same id or relies on either CSS-in-JS tools or CSS naming strategies , shadow DOM has the potential to improve your developer experience. For a full list of CSS inheritable properties, check out this answer on Stack Overflow. Suddenly any change, no matter how small, has to be repeated across all those files. Open Web Components — Guides, tools and libraries for developing web components. ShadowRoot Represents the root node of a shadow DOM subtree.

The ‘oncontentchange’ event fires when the element to which the Component is attached has been parsed, or whenever the content of the element changes. Of course, application UIs are dynamic and change over time. In the next section, we will introduce a new concept of “state”. State allows React components to change their output over time in response to user actions, network responses, and anything else, without violating this rule. Extracting components might seem like grunt work at first, but having a palette of reusable components pays off in larger apps. A good rule of thumb is that if a part of your UI is used several times , or is complex enough on its own , it is a good candidate to be extracted to a separate component.

Defining Methods – the Element

The functionality of a custom element is defined using an ES2015 class which extends HTMLElement. Extending HTMLElement ensures the custom element inherits the entire DOM API and means any properties/methods that you add to the class become part of the element’s DOM interface. Essentially, use the class to create a public JavaScript API for your tag. This article introduces the use of the Custom Elements API.

If your project transpiles to or uses ES5, be sure to see the notes on including custom-elements-es5-adapter.js in addition to the polyfills. Overwriting an element’s children with new content is generally not a good idea because it’s unexpected.

Componentizing Web Applications

Another possible use for HTCs is to provide cross-domain scripting access; the HTC could declare which properties, methods and events are allowed to be accessed from outside the domain. The customElements global defines useful methods for working with custom elements. With Custom Elements, web developers can create new HTML tags, beef-up existing HTML tags, or extend the components other developers have authored. It brings a web standards-based way to create reusable components using nothing more than vanilla JS/HTML/CSS. The result is less code, modular code, and more reuse in our apps. In the next article, we will take a deeper look at the HTML templates part of this. Then, we’ll follow that up with a discussion of custom elements and shadow DOM.

• Use your custom element wherever you like on your page, just like you would any regular HTML element.
• This series assumes a basic understanding of HTML, CSS, and JavaScript.
• For our new huge long-term enterprise project we have chosen web components and vanilla JS instead of frameworks for UI.
• Now that the footer component is encapsulated within its own Shadow DOM, it no longer has access to the Font Awesome CDN link in index.html.
• An HTML Attribute sets either style or layout or content related information for an HTML Element.

Such functions are called “pure” because they do not attempt to change their inputs, and always return the same result for the same inputs. This component can be tricky to change because of all the nesting, and it is also hard to reuse individual parts of it. Typically, new React apps have a single App component at the very top. However, if you integrate React into an existing app, you might start bottom-up with a small component like Button and gradually work your way to the top of the view hierarchy. Except as otherwise noted, the content of this page is licensed under the Creative Commons Attribution 4.0 License, and code samples are licensed under the Apache 2.0 License. If you happen to be interested in the old v0 spec, check out the html5rocks article.

Nested HTML Elements

Don’t be afraid to split components into smaller components. The above two components are equivalent from React’s point of view. That part of the spec was deprecated and will NOT be used going forward. HTML Imports used to be part of the Web Component spec but has been deprecated and was replaced with ES6 module imports. Might be worth adding a warning so people don’t XSS themselves .

Similarly, you’ll receive a disconnectedCallback() right after your element is removed from the DOM (e.g. the user calls el.remove()). What’s more, these components can generally be used out-of-the-box with today’s most popular frameworks, including Angular, React, Vue, and others with minimal effort. This series assumes a basic understanding of HTML, CSS, and JavaScript. If you feel weak in one of those areas, don’t worry, building a custom element actually simplifies many complexities in front-end development. Components/footer.jsOne thing to note is, while it seems like you’re causing the browser to load Font Awesome twice , browsers are smart enough not to fetch the same resource again. By extending the generic HTMLElement class, you can create any kind of element you want.

HTML Components are a legacy technology used to implement components in script as Dynamic HTML “behaviors” in the Microsoft Internet Explorer web browser. Such files typically use an .htc extension and the “text/x-component” MIME type. Cross-browser for creating and extending reusable components.