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Web Component Base
🤷♂️ zero-dependency, 🤏 tiny JS base class for creating reactive custom elements easily ✨
When you extend the WebComponent class for your component, you only have to define the template and properties. Any change in any property value will automatically cause just the component UI to render.
The result is a reactive UI on property changes. View on CodePen ↗
Features
- A props API that synchronizes your components' property values and HTML attributes
- Sensible life-cycle hooks that you understand and remember
- An html tagged templates powered by preact's html/mini
- Attach functions as "side effects" that gets triggered on property value changes with attachEffect (example)
- Provided out-of-the-box with McFly, a powerful no-framework framework
Table of Contents
- Installation
- Usage
templatevsrender()- Prop access
- Quick Start Example
- Life-Cycle Hooks
onInit- the component is connected to the DOM, before view is initializedafterViewInit- after the view is first initializedonDestroy- the component is disconnected from the DOMonChanges- every time an attribute value changes
- Library Size
Installation
The library is distributed as complete ESM modules, published on NPM. Please file an issue in our issue tracker for problems or requests regarding our distribution.
Import via unpkg (no bundlers needed!)
Import using unpkg in your vanilla JS component. We will use this in the rest of our usage examples.
Please check
import { WebComponent } from "https://unpkg.com/web-component-base@latest/index.js";
Installation via npm
Usable for projects with bundlers or using import maps pointing to to the specific files in downloaded in your node_modules/web-component-base.
npm i web-component-base
Usage
In your component class:
// HelloWorld.mjs
import { WebComponent } from "https://unpkg.com/web-component-base@latest/index.js";
class HelloWorld extends WebComponent {
static props ={
myName: 'World',
emotion: 'sad'
}
get template() {
return `
<h1>Hello ${this.props.myName}${this.props.emotion === "sad" ? ". 😭" : "! 🙌"}</h1>
`;
}
}
customElements.define('hello-world', HelloWorld);
In your HTML page:
<head>
<script type="module" src="HelloWorld.mjs"></script>
</head>
<body>
<hello-world my-name="Ayo" emotion="sad">
<script>
const helloWorld = document.querySelector('hello-world');
setTimeout(() => {
helloWorld.setAttribute('emotion', 'excited');
}, 2500)
</script>
</body>
The result is a reactive UI that updates on attribute changes:
template vs render()
This mental model attempts to reduce the cognitive complexity of authoring components:
- The
templateis a read-only property (initialized with agetkeyword) that represents how the component view is rendered. - There is a
render()method that triggers a view render. - This
render()method is automatically called under the hood every time an attribute value changed. - You can optionally call this
render()method at any point to trigger a render if you need (eg, if you have private unobserved properties that need to manually trigger a render) - Overriding the
render()function for handling a customtemplate--where you can returnstring | Node | (string | Node)[]is also an option. More examples on this to follow.
Prop Access
The props property of the WebComponent interface is provided for easy read/write access to a camelCase counterpart of any observed attribute.
class HelloWorld extends WebComponent {
static props = {
myProp: 'World'
}
get template() {
return html`
<h1>Hello ${this.props.myProp}</h1>
`;
}
}
Assigning a value to the props.camelCase counterpart of an observed attribute will trigger an "attribute change" hook.
For example, assigning a value like so:
this.props.myName = 'hello'
...is like calling the following:
this.setAttribute('my-name','hello');
Therefore, this will tell the browser that the UI needs a render if the attribute is one of the component's observed attributes we explicitly provided with static props;
Note
The
propsproperty ofWebComponentworks likeHTMLElement.dataset, exceptdatasetis only for attributes prefixed withdata-. A camelCase counterpart usingpropswill give read/write access to any attribute, with or without thedata-prefix. Another advantage overHTMLElement.datasetis thatWebComponent.propscan hold primitive types 'number', 'boolean', 'object' and 'string'.
Alternatives
The current alternatives are using what HTMLElement provides out-of-the-box, which are:
HTMLElement.datasetfor attributes prefixed withdata-*. Read more about this on MDN.- Methods for reading/writing attribute values:
setAttribute(...)andgetAttribute(...); note that managing the attribute names as strings can be difficult as the code grows.
Quick Start Example
Here is an example of using a custom element in a single .html file.
<!DOCTYPE html>
<html lang="en">
<head>
<title>WC Base Test</title>
<script type="module">
import { WebComponent } from "https://unpkg.com/web-component-base@latest/index.js";
class HelloWorld extends WebComponent {
static props = {
myName: 'World'
}
get template() {
return `<h1>Hello ${this.props.myName}!</h1>`;
}
}
customElements.define("hello-world", HelloWorld);
</script>
</head>
<body>
<hello-world my-name="Ayo"></hello-world>
<script>
const helloWorld = document.querySelector('hello-world');
setTimeout(() => {
helloWorld.props.myName = 'Ayo zzzZzzz';
}, 2500);
</script>
</body>
</html>
Life-Cycle Hooks
Define behavior when certain events in the component's life cycle is triggered by providing hook methods
onInit()
- Triggered when the component is connected to the DOM
- Best for setting up the component
import { WebComponent } from "https://unpkg.com/web-component-base@latest/index.js";
class ClickableText extends WebComponent {
// gets called when the component is used in an HTML document
onInit() {
this.onclick = () => console.log(">>> click!");
}
get template() {
return `<span style="cursor:pointer">Click me!</span>`;
}
}
afterViewInit()
- Triggered after the view is first initialized
class ClickableText extends WebComponent {
// gets called when the component's innerHTML is first filled
afterViewInit() {
const footer = this.querySelector('footer');
// do stuff to footer after view is initialized
}
get template() {
return `<footer>Awesome site © 2023</footer>`;
}
}
onDestroy()
- Triggered when the component is disconnected from the DOM
- best for undoing any setup done in
onInit()
import { WebComponent } from "https://unpkg.com/web-component-base@latest/index.js";
class ClickableText extends WebComponent {
clickCallback() {
console.log(">>> click!");
}
onInit() {
this.onclick = this.clickCallback;
}
onDestroy() {
console.log(">>> removing event listener");
this.removeEventListener("click", this.clickCallback);
}
get template() {
return `<span style="cursor:pointer">Click me!</span>`;
}
}
onChanges()
- Triggered when an attribute value changed
import { WebComponent } from "https://unpkg.com/web-component-base@latest/index.js";
class ClickableText extends WebComponent {
// gets called when an attribute value changes
onChanges(changes) {
const {property, previousValue, currentValue} = changes;
console.log('>>> ', {property, previousValue, currentValue})
}
get template() {
return `<span style="cursor:pointer">Click me!</span>`;
}
}
Library Size
All the functions and the base class in the library are minimalist by design and only contains what is needed for their purpose.
As of the major release v2.0.0, the base class is around 1.7 kB (min + gzip) according to bundlephobia.com and 1.1 kB (min + brotli) according to size-limit. There is an increase in size before this release -- primarily for advanced features in building complex applications.
Note
As a builder of both simple sites and complex web apps, I recognize that not all custom elements need advanced features for reactivity.
I also don't want to get things in my code that I don't need (YAGNI -- You Aren't Gonna Need It)... and I want a base class for simpler use cases that don't have Proxy props or attaching effects...
To address this, I am working on a "lite" version my base class... please stay tuned.
-Ayo