# Web Component Base
[](https://www.npmjs.com/package/web-component-base)
[](https://www.npmjs.com/package/web-component-base)
[](https://www.npmjs.com/package/web-component-base)
[](https://bundlephobia.com/package/web-component-base)
> A zero-dependency, ~600 Bytes (minified & gzipped), 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.
Table of Contents
- Import via unpkg
- Installation via npm
- Usage
- `template` vs `render()`
- Prop access
- Alternatives
- Quick Start Example
- Life-Cycle Hooks
- `onInit` - the component is connected to the DOM, before view is initialized
- `afterViewInit` - after the view is first initialized
- `onDestroy` - the component is disconnected from the DOM
- `onChanges` - every time an attribute value changes
- Library Size
## Import via unpkg
Import using [unpkg](https://unpkg.com/web-component-base) in your vanilla JS component. We will use this in the rest of our [usage examples](#usage).
```js
import WebComponent from "https://unpkg.com/web-component-base@latest/WebComponent.min.js";
```
## Installation via npm
Usable for projects with bundlers or using import maps.
```bash
npm i web-component-base
```
## Usage
In your component class:
```js
// HelloWorld.mjs
import WebComponent from "https://unpkg.com/web-component-base@latest/WebComponent.min.js";
class HelloWorld extends WebComponent {
static properties = ["my-name", "emotion"];
get template() {
return `
Hello ${this.props.myName}${this.props.emotion === "sad" ? ". ðŸ˜" : "! 🙌"}
`;
}
}
customElements.define('hello-world', HelloWorld);
```
In your HTML page:
```html
```
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:
1. The `template` is a read-only property (initialized with a `get` keyword) that represents *how* the component view is rendered.
1. There is a `render()` method that triggers a view render.
1. This `render()` method is *automatically* called under the hood every time an attribute value changed.
1. You can *optionally* call this `render()` method at any point to trigger a render if you need.
## Prop Access
The `WebComponent.props` read-only property is provided for easy access to *any* observed attribute.
This API gives us read/write access to any attribute properties:
```js
class HelloWorld extends WebComponent {
static properties = ["my-prop"];
onInit() {
let count = 0;
this.onclick = () => this.props.myProp = `${++count}`
}
get template() {
return `
Hello ${this.props.myProp}
`;
}
}
```
Assigning value to the `props.camelCase` counterpart 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 properties = ['my-name']`;
> This works like [`HTMLElement.dataset`](https://developer.mozilla.org/en-US/docs/Web/API/HTMLElement/dataset), except `dataset` is only for attributes prefixed with `data-*`. A camelCase counterpart using `props` will give read/write access to any attribute, with or without the `data-*` prefix.
### Alternatives
The current alternatives are using what `HTMLElement` provides out-of-the-box, which are:
1. `HTMLElement.dataset` for attributes prefixed with `data-*`
1. Methods for reading/writing attribute values: `setAttribute(...)` and `getAttribute(...)`; 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:
```html
WC Base Test
```
## 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
```js
import WebComponent from "https://unpkg.com/web-component-base@latest/WebComponent.min.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 `Click me!`;
}
}
```
### afterViewInit()
- Triggered after the view is first initialized
```js
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 ``;
}
}
```
### onDestroy()
- Triggered when the component is disconnected from the DOM
- best for undoing any setup done in `onInit()`
```js
import WebComponent from "https://unpkg.com/web-component-base@latest/WebComponent.min.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 `Click me!`;
}
}
```
### onChanges()
- Triggered when an attribute value changed
```js
import WebComponent from "https://unpkg.com/web-component-base@latest/WebComponent.min.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 `Click me!`;
}
}
```
## Library Size
The bundle size was reported to be 587 Bytes (minified & gzipped) by [bundlephobia](https://bundlephobia.com/package/web-component-base). Running [size-limit](https://npmjs.com/package/@size-limit/preset-small-lib) reports the base class size as around 760 Bytes (minified & brotlied), and using the `WebComponent.min.js` version gets it down to around 400 Bytes.