@lume/element

Easily and concisely write Custom Elements with simple templates and reactivity.

Use the custom elements on their own in plain HTML or vanilla JavaScript, or in Vue, Svelte, Solid.js, Stencil.js, React, and Preact, with full type checking, autocompletion, and intellisense in all the template systems of those frameworks, in any IDE that supports TypeScript such as VS Code.

Write your elements once, then use them in any app, with a complete developer experience no matter which base component system your app uses.

`npm install @lume/element`

💡Tip:

If you are new to Custom Elements, first learn about the basics of Custom Element APIs available natively in browsers. Lume Element simplifies the creation of Custom Elements compared to writing them with vanilla APIs, but sometimes vanilla APIs are all that is needed.

Live demos

Lume 3D HTML (The landing page, all of Lume's 3D elements, and the live code editors themselves in the doc pages)
CodePen, html template tag, no decorators
Stackblitz with Babel, JSX, decorators
Stackblitz with Vite, JSX, TypeScript, decorators
Solid Playground, TypeScript, no decorators

Cliché Click Counter Example
Intro
Basic Usage
API
- Element
- Decorators
Runtime Type Checking
TypeScript
Resources
Status

Cliché Click Counter Example

Define a <click-counter> element:

import {Element, element, numberAttribute} from '@lume/element'
import html from 'solid-js/html'
import {createEffect} from 'solid-js'

@element
class ClickCounter extends Element {
  @numberAttribute count = 0

  template = () => html`<button onclick=${() => this.count++}>Click! (count is: ${() => this.count})</button>`

  css = `
		button {
			border: 2px solid deeppink;
			margin: 5px;
		}
	`

  // Log the `count` any time it changes:
  @effect logCount() {
    console.log('count is:', this.count)
  }
}

Use the <click-counter> in a plain HTML file:

<body>
  <click-counter></click-counter>

  <!-- Manually set the `count` value in HTML: -->
  <click-counter count="100"></click-counter>

  <script type="module">
    import './click-counter.js'

    // Manually set the `count` value in JS:
    document.querySelector('click-counter').count = 200
  </script>
</body>

Example on CodePen (without decorators)

Note

Once decorators land in browsers, the above example will work out of the box as-is without compiling, but for now a compile step is needed for using decorators.

JSX can be used for the template of an element, but that will always require compiling:

template = () => <button> Click! (count is: {this.count}) </button>

Further examples below show how to define elements without decorators or JSX, which works today without a compiler.

Use the <click-counter> in another element's template,

import {Element, element} from '@lume/element'
import html from 'solid-js/html'
import {signal} from 'classy-solid'

@element('counter-example')
class CounterExample extends Element {
  @signal count = 50 // Not an attribute, only a signal.

  template = () => html`<click-counter count=${() => this.count}></click-counter>`
}

document.body.append(new CounterExample())

Use <click-counter> in a plain function component (i.e. a Solid.js component):

// At this point this, this boils down to plain Solid.js code (`@lume/element` comes
// with `solid-js`)

import {createSignal} from 'solid-js'
import html from 'solid-js/html'

function CounterExample() {
  const [count, setCount] = createSignal(50)

  return html`<click-counter count=${count()}></click-counter>`
}

document.body.append(CounterExample())

Intro

Custom Elements (also known as Web Components are a feature of browsers that allow us to define new HTML elements that the browser understands in the same way as built-in elements like <div> or <button>. They are very useful for organizaing web apps into separately and sometimes re-usable pieces (elements).

If that flew over your head then you might first want to try a beginner HTML tutorial. You will also need to some basic knowledge of JavaScript.

@lume/element provides a set of features that make it easier to manipulate elements and to define new custom elements and easily compose them together into an application.

With @lume/element we can create custom elements that have the following features:

Reactive instance properties that receive values from element attributes of the same name (but dash-cased).
Declarative templates, written with JSX or html template tag, that automatically update when reactive instance properties are used in the templates.
Scoped styling with or without a ShadowRoot.
Decorators for concise element definitions.

A more detailed feature description:

Element attributes are defined with @attribute decorators on class fields.
- Class fields decorated with @attribute receive values from HTML attributes (with the same name but dash-cased) when the HTML attribute values change.
- Decorators are powered by classy-solid: utilities for using Solid.js patterns on classes, such as the @signal decorator for making class fields reactive (backed by Solid signals). Decorators from @lume/element compose the @signal decorator to make properties be reactive.
- As decoraators are not out in browsers yet, an alternative non-decorator API can be used, which does not require a build.
Each custom element can have an HTML template that automatically updates the DOM when any reactive variables used in the template changes.
- Templates can be written in the form of HTML-like markup inside JavaScript called JSX, specifically the JSX flavor from Solid.js. This requires a build step.
- Templates can also be written using Solid's html template string tag, which does not require a build step.
- When a template updates, the whole template does not re-run, only the part of the template where a variable changed is updated, and only that particular piece of DOM gets modified. There is no (expensive) virtual DOM diffing.
- Because changes to HTML attributes on an element map to properties backed by signals on the element instance, this will cause the custom element's template to update if its template uses those properties.
Custom element styles are automatically scoped, similar to Vue, Svelte, and other systems with style scoping.
- If you're familiar with custom elements, you know that the browser gives this to us for free when using ShadowDOM.
- If you opt an element out of having a ShadowRoot, @lume/element applies its own style scoping for the element at the nearest root node.

Install and Setup

STUB: This section needs expansion, but should be enough for anyone familiar with common build tooling in the webdev/JS ecosystem. Contributions very welcome!

CDN method (easiest, no compiler or command line needed)

Follow the guide on installing lume from CDN, but simply replace lume with @lume/element. The process is otherwise the same.

The examples here in the README follow the CDN approach to keep things simple, for example.

[!Note] Decorator syntax and JSX syntax are both not supported with this install method as it does not use a build step. In the near future, decorators will be out natively in browsers and JS engines (but not JSX).

Local install with build

This assumes some familiarity with command lines and JavScript build tools.

First make sure Node.js is installed so that we have the npm package manager avaiable.

Install the @lume/element package using the following in a terminal:

npm install @lume/element

In order to use decorators today (recommended), we need to compile them with TypeScript 5 or higher (recommended, even if writing JS and not TS, as decorator syntax works out of the box with TypeScript), or use the Babel compiler with @babel/plugin-proposal-decorators.

npm install --save-dev typescript
# or
npm install --save-dev @babel/cli @babel/core @babel/plugin-proposal-decorators

If using TypeScript, set allowJs in tsconfig.json to allow compiling JS files, f.e.:

{
	"compilerOptions": {
		"allowJs": true,
		"outDir": "dist"
	},
	"include": ["./src/**/*"]
}

and running npx tsc. See the TypeScript section below for configuring JSX types for various frameworks (Solid, React, Preact, etc).

If using Babel, add the decorators plugin to .babelrc, f.e.

{
  "plugins": ["@babel/plugin-proposal-decorators"]
}

and running npx babel src --out-dir dist.

If you'd like to use the HTML-like markup inside JavaScript known as "JSX", instead of Solid's html template tag which requires no build, the babel-preset-solid package will also be needed:

npm install --save-dev babel-preset-solid

Configure Babel to use the preset inside your project's .babelrc file or in your Webpack babel-loader config:

{
  "plugins": ["@babel/plugin-proposal-decorators"],
  "presets": ["solid"]
}

[!Note] If compiling decorators with TypeScript, Babel is still needed for Solid JSX because TypeScript does not compile JSX into Solid.js format, only into React format. Either compile decorators with TypeScript and have Babel compile JSX in a second step, or compile both decorators and JSX with Babel in a single step.

Basic Usage

Create custom elements

A great way to create re-usable components is to create Custom Elements. The advantage of custom elements is that they follow web standards, and therefore they can be used in any web application and manipulated by any DOM manipulation libraries like jQuery, React, Vue, Svelte, or Angular, Solid.js, and all the rest.

The following is a custom element definition with a reactive property firstName that also accepts values from an attribute named first-name (the property name is converted to dash-case for the attribute name).

Note

Deorators and JSX are not required. The non-decorator and non-JSX forms are shown further below. The Decorators section has details on each decorator available.

import {
  Element, // A base class for LUME custom elements
  element, // A decorator for defining elements, required for reactive JS properties.
  attribute, // A property decorator to map attributes to properties, and that makes properties reactive
  eventAttribute, // A property decorator that causes values from the attributes/properties to be set as an event listener for the respective event, just like built-in "onclick" attributes/properties.
  css, // A no-op identity template tag function (useful to enable CSS syntax highlighting in various text editors)

  // Decorators for defining specific attributes types (string values are coerced to the respective JS type):
  stringAttribute,
  numberAttribute,
  booleanAttribute,
} from '@lume/element'

@element('greeting-card') // defines the element tag name
class GreetingCard extends Element {
  // The firstName property will be a reactive variable, and any value from an
  // attribute named 'first-name' will be mapped back to this property (the
  // attribute name is the dash-case version of the property name).
  @attribute firstName = 'Roger'

  // Specific attribute types (the JS property will always be of the specified
  // type):
  @stringAttribute someString = ''
  @numberAttribute someNumber = 123
  @booleanAttribute someBoolean = false

  // Define event properties to specify which events the element dispatches.
  // Besides being useful for type definitions in JSX, these properties work
  // like the builtin event properties such as "onclick" (JS property or DOM
  // attribute code string).
  //
  // For example, a user can write `el.onhello = event => {...}` just like
  // they can do with builtin event properties like `el.onclick = event =>
  // {...}`.
  @eventAttribute onhello = null

  // Define a DOM tree that we want rendered on screen by providing a
  // `template`. The `template` should be a function that returns a DOM
  // element or array of DOM elements (which we can create with JSX, or with
  // an `html` template tag, or with plain JS). The DOM content will be, by
  // default, appended into the ShadowRoot of our custom element.
  //
  // To take advantage of reactivity in our template, simply interpolate
  // properties that were decoratored with an attribute decorator or defined
  // with `static observedAttributeHandlers` into the template.
  //
  // Here, any time the `.firstName` property's value changes, the DOM will be
  // automatically updated.
  template = () => (
    <div>
      <span>
        Hello <i>{this.firstName}</i>
      </span>
      {/* Children of a <greeting-card> element get rendered here. */}
      <slot></slot>
    </div>
  )

  // Apply styling to this element and its content with the static `css` property.
  // Because the property is static, this style is re-used across all instances of the element.
  // Styles are by default scoped to the element's content due to ShadowRoot style encapsulation.
  static css = css`
    :host {
      background: skyblue;
    }
    div {
      color: pink;
    }
  `

  // For instance-specific styling, use the non-static `css` property.  This
  // style has higher precedence over styles in the `static css` property.  In
  // this example, the divs in each instance of this element will have borders
  // of random sizes.  Note, `css` is currently not reactive, it runs once
  // initially, so using a reactive property in the css will currently not
  // update the style.
  css = css`
    div {
      border: ${Math.random() * 5}px solid teal;
    }
  `

  // connectedCallback is a method that fires any time this custom element is
  // connected into a web site's live DOM tree.
  connectedCallback() {
    super.connectedCallback() // Don't forget to call the super method!

    // Once the element is connected, let's update the `.firstName` prop after a
    // couple of seconds, and we'll see the change on screen.
    setTimeout(() => (this.firstName = 'Zaya'), 2000)

    // And show that it works by setting HTML attributes too, two seconds later.
    setTimeout(() => this.setAttribute('first-name', 'Raquel'), 4000)

    // The element may dispatch events.
    setTimeout(() => this.dispatchEvent(new Event('hello')), 3000)
  }

  // Use the disconnectedCallback to clean anything up when the element is removed from the DOM.
  disconnectedCallback() {
    super.disconnectedCallback()
    // ... clean up ...
  }
}

Now we can use it in the HTML of a web site, or in the template of another component:

<greeting-card first-name="Raynor" onhello={() => console.log(event.target.firstName, 'says hello')}></greeting-card>

Example on CodePen (without decorators, with Solid's html template tag instead of JSX)

Inside an element's template() method we can assign bits and pieces of DOM to variables, and we can also use other custom elements and functional components. Similary, the css property can also be a method:

@element('greeting-card')
class GreetingCard extends Element {
  // ... same as before ...

  // This time 'template' is a method that has some logic, and refers to pieces of DOM using variables.
  template() {
    const greeting = (
      <span>
        Hello <i>{this.firstName}</i>
      </span>
    )

    console.log(greeting instanceof HTMLSpanElement) // true

    // One piece of DOM can be composed into another:
    const result = <div>{greeting}</div>

    console.log(result instanceof HTMLDivElement) // true

    return result
  }

  // ... same as before ...

  css() {
    const thickness = Math.random() * 5

    return css`
      div {
        border: ${thickness}px solid teal;
      }
    `
  }

  // ... same as before ...
}

Easily create and manipulate DOM

Lume Element is built on Solid.js, so we can also use Solid.js at the top level of a module for example. This sort of code can be useful in the template of a custom element, or the body of a functional component.

import {createSignal} from 'solid-js'

// Make a signal with an initial value of 0.
const [count, setCount] = createSignal(0)

// Increment the value of count every second.
setInterval(() => setCount(count() + 1), 1000)

// Create a <div> element with a child <h1> element. The data-count attribute
// and the text content of the <h1> element will automatically be updated whenever
// the count variable changes.
const el = (
  <div>
    <h1 data-count={count()}>The count is: {count()}</h1>
  </div>
)

// The result stored in the `el` variable is a `<div>` element! For example,
// we can call regular DOM APIs like `setAttribute` on it.
el.setAttribute('foo', 'bar')

// Append the element to the body of the page, and now we'll see a
// continually-updating message on the screen.
document.body.append(el)

Example on CodePen (with Solid's html template tag instead of JSX)

Create functional components

Continuing with the same count variable from the previous example, here's how to compose DOM trees using "functional components". This is plain Solid.js, and functional components (Solid.js components) can be used in a custom element's template.

A functional component is a function that simply returns one or more DOM elements. JSX expressions and the html template string tag both return the top level elements defined in the markup.

// This is just plain Solid.js code. See https://solidjs.com for more on writing
// functional components.

// This Label functional component uses the empty <></> tag to contain more than
// one root-level child, and the return value will be an array of DOM nodes.
const Label = props => (
  <>
    <div>{props.greeting}</div>
    {props.children}
  </>
)

// This Greeting functional component nests the content of the Label component
// in its template, and the <div> inside the <Label> gets distributed to the
// part of the Label component where we see `{props.children}`.
const Greeting = () => (
  <section>
    <Label greeting={'hello (' + count() + ')'}>
      <div>John</div>
    </Label>
  </section>
)

// The `Greeting` function only needs to be called once, and it will return a
// reference to an element or multiple elements. The `Greeting` function does
// NOT need to be called over and over to re-render like in some other libraries
// (for example React). That's what makes all of this simple and clean. The
// reactivity inside the component templates takes care of updating content of
// the created DOM tree.
// Here `elem` will be a reference to an actual `<section>` element that the
// `Greeting` function returned.
const elem = Greeting()

// It's just DOM! Use regular DOM APIs to append the element to the body.
document.body.append(elem)

Example on CodePen (with Solid's html template tag instead of JSX)

Using functional components inside custom elements

Continuing from above, here's a custom element that re-uses the Greeting component. This shows that any regular Solid.js component can be used in the template of a custom element made with @lume/element:

@element // The 'cool-element' name is implied from the constructor name (dash-cased)
class CoolElement extends Element {
  template = () => (
    <>
      <h2>Here's a greeting:</h2>
      <Greeting />
    </>
  )
}

document.body.insertAdjacentHTML('beforeend', `<cool-element></cool-element>`)

Example on CodePen (without decorators, with Solid's html template tag instead of JSX)

Functional components vs custom elements

Writing function components can sometimes be simpler, but functional components do not have features that custom elements have such as native style scoping (style scoping with function components requires an additional Solid.js library or compiler plugin), etc.

In contrast to custom elements, functional components only work within the context of other functional components made with Solid.js or custom elements made with @lume/element. Functional components are not compatible with HTML, React, Vue, Angular, Svelte, or all the other web libraries and frameworks. For portability across applications and frameworks, this is where custom elements shine.

Custom elements are also debuggable in a browser's element inspector out of the box, while functional components are not (functional components require devtools plugins for each browser, if they even exist). See Lume's Debugging guide for an example.

API

`Element`

A base class for custom elements made with @lume/element.

Note

The Element class from @lume/element extends from HTMLElement.

Safari does not support customized built-ins, and neither does @lume/element, so at the moment we do not support extending from other classes such as HTMLButtonElement, etc.

The Element class provides:

`static elementName`

The default tag name of the elements that are instances of this class.

This field is optional: if not provided the element tag name will default to the dash-cased version of the class name. For example instances of a class CoolElement will be written with the <cool-element> tag in HTML.

When using the @element decorator, this field's value will be used if an element name is not passed to the decorator.

@element
class SomeEl extends LumeElement {
  static elementName = 'some-el'
}

console.log(document.createElement('some-el') instanceof SomeEl) // true

@element
class CoolEl extends LumeElement {
  // static elementName omitted
}

console.log(document.createElement('cool-el') instanceof CoolEl) // true

@element
class SaucyElement extends LumeElement {
  static elementName = 'juicy-el'
}

console.log(document.createElement('juicy-el') instanceof SaucyElement) // true

Example on CodePen

`template`

A subclass can define a .template that returns a DOM node, and this DOM node will be appened into the element's ShadowRoot by default, or to the element itself if .hasShadow is false.

One way to write a template is using Solid JSX syntax (this will always require a build step).

import {Element} from '@lume/element'
import {createSignalFunction} from 'classy-solid' // a small wrapper around Solid's createSignal that allows reading and writing from the same function.

class CoolElement extends Element {
  count = createSignalFunction(100)

  template = () => (
    <div>
      <span>The count is: {this.count()}!</span>
    </div>
  )
  // ...
}

customElements.define('cool-element', CoolElement)

Another way to write a template is using Solid's html template string tag (which does not require a build step). Using the following template, the example can run in a browser without a compile step (note, we're not using decorators yet):

// ...
template = () => html`
  <div>
    <span>The count is: ${this.count}!</span>
  </div>
`
// ...

Example on CodePen (with html template tag instead of JSX)

Note

When count changes, the template updates automatically.

We can also manually create DOM any other way, for example here we make and return a DOM tree using DOM APIs, and using a Solid effect to update the element when count changes (but we could have used React or jQuery, or anything else!):

// ...same...

import {createEffect} from 'solid-js'

// ...same...

// Replace the previous `template` with this one:
template = () => {
  const div = document.createElement('div')
  const span = document.createElement('span')
  div.append(span)

  createEffect(() => {
    // Automatically set the textContent whenever `count` changes (this is a
    // conceptually-simplified example of what Solid JSX compiles to).
    span.textContent = `The count is: ${this.count()}!`
  })

  return div
}

// ...same...

Example on CodePen

`static css`

Use the static css field to define a CSS string for styling all instances of the given class. A static property allows @lume/element to optimize by sharing a single CSSStyleSheet across all instances of the element, which could be beneficial for performance if there are many thousands of instances.

import {Element} from '@lume/element'

class CoolElement extends Element {
  template = () => <span>This is some DOM!</span>

  // Style is scoped to our element, this will only style the <span> inside our element.
  static css = `
    span { color: violet; }
  `
}

customElements.define('cool-element', CoolElement)

Example on CodePen (with html template tag instead of JSX)

The static css property can also be a function:

// ...

class CoolElement extends Element {
  // ...
  static css = () => {
    const color = 'limegreen'

    return `
      span { color: ${color}; }
    `
  }
  // ...
}

Example on CodePen (with html template tag instead of JSX)

💡Tip:

Use the css identity template tag to enable syntax highlighting and code formatting in some IDEs:

import {css} from '@lume/element'
// ...

class CoolElement extends Element {
  // ...
  static css = css`
    span {
      color: cornflowerblue;
    }
  `
  // ...
}

`css`

Use the non-static css property to define styles that are applied per instance of the given element. This is useful for style that should differ across instances. This will not be as optimized as static css will be because it will create one stylesheet per element instance, but the performance difference will not matter for most use cases.

import {Element, css} from '@lume/element'

class CoolElement extends Element {
  template = () => <span>This is some DOM!</span>

  // A random color per instance.
  #color = `hsl(calc(${Math.random()} * 360) 50% 50%)`

  // Style is scoped to our element, this will only style the <span> inside our element.
  css = css`
    span {
      color: ${this.#color};
    }
  `
}

Example on CodePen (with html template tag instead of JSX)

`static observedAttributes`

Nothing new here, this is simply a part of the browser's native Custom Elements static observedAttributes API. It defines which attributes will be observed. From the previous example:

class CoolElement extends Element {
  static observedAttributes = ['foo', 'bar']
  // ...
}

Note! Although static observedAttributes works, it is recommended to use the static observedAttributeHandlers property instead:

`static observedAttributeHandlers`

This is an alternative to attribute decorators (recommended, see the Decorators docs below), and will be removed after decorators are supported natively in JS engines.

As an alternative to static observedAttributes, and mainly for non-decorator users (because not all JS engines support them yet at time of writing this), observed attributes can be defined with static observedAttributeHandlers, a map of attribute names to attribute handlers. This requires using the @element decorator (calling it as a plain function for non-decorator usage). This will map attributes to JS properties and make the JS properties reactive.

static observedAttributeHandlers is an object where each key is a property name to be associated with an attribute, and each value is an object with the following shape:

/**
 * Defines how values are mapped from an attribute to a JS property on a custom
 * element class.
 */
export type AttributeHandler<T = any> = {
  // TODO The `to` handler currently does nothing. In the future, if there is demand
  // for it, this will be for property-to-attribute reflection.
  to?: (propValue: T) => string | null

  /**
   * Define how to deserialize an attribute string value on its way to the
   * respective JS property.
   *
   * If not defined, the attribute string value is passed to the JS property
   * untouched.
   *
   * **Default when omitted:** `value => value`
   */
  from?: (AttributeValue: string) => T

  /**
   * A side effect to run when the value is set on the JS property. It also
   * runs on with the initial value. Avoid this if you can, and instead use
   * effects. One use case of this is to call addEventListener with event
   * listener values, just like with native `.on*` properties.
   *
   * **Default when omitted:** `() => {}` (no sideeffect)
   */
  sideEffect?: (instance: Element, prop: string, propValue: T) => void

  /**
   * @deprecated - Define a field with the initial value instead of providing
   * the initial value here. When decorators land in browsers, this will be
   * removed.
   *
   * The default value that the respective JS property should have when the
   * attribute is removed.
   *
   * If this is not specified, and the respective class field is defined, it
   * will default to the initial value of the class field.  If this is
   * specified, it will take precedence over the respective field's initial
   * value. This should generally be avoided, and the class field initial
   * value should be relied on as the source of the default value.
   *
   * When defined, an attribute's respective JS property will be set to this
   * value when the attribute is removed. If not defined, then the JS property
   * will always receive the initial value of the respective JS class field or
   * `undefined` if the field was not defined (that's the "initial value" of
   * the field), when the attribute is removed.
   *
   * **Default when omitted:** the value of the respective class field, or
   * `undefined` if the field was not defined.
   */
  default?: T

  /**
   * Whether to convert the property name to dash-case for the attribute name.
   * This option is ignore if the `name` option is set.
   *
   * The default is `true`, where the attribute name will be the same as the
   * property name but dash-cased (and all lower case). For example, `fooBar`
   * becomes `foo-bar` and `foo-bar` stays `foo-bar`.
   *
   * If this is set to `false`, the attribute name will be the same as the
   * property name, but all lowercased (attributes are case insensitive). For
   * example `fooBar` becomes `foobar` and `foo-bar` stays `foo-bar`.
   *
   * Note! Using this option to make a non-standard prop-attribute mapping
   * will result in template type definitions (f.e. in JSX) missing the
   * customized attribute names and will require custom type definition
   * management.
   *
   * **Default when omitted:** `true`
   */
  dashcase?: boolean

  /**
   * The name of the attribute to use. Use of this options bad practice to be
   * avoided, but it may be useful in rare cases.
   *
   * If this is not specified, see `dashcase` for how the attribute name is
   * derived from the property name.
   *
   * Note! Using this option to make a non-standard prop-attribute mapping
   * will result in template type definitions (f.e. in JSX) missing the
   * customized attribute names and will require custom type definition
   * management.
   *
   * **Default when omitted:** the attribute name derived from the property
   * name, converted to dash-case based on the `dashcase` option.
   */
  name?: string

  /**
   * Whether to suppress warnings about the attribute attribute name clashes
   * when not using default `dashcase` and `name` settings. This is
   * discouraged, and should only be used when you know what you're doing,
   * such as overriding a property that has `dashcase` set to `false` or
   * `name` set to the same name as the attribue of another property.
   *
   * **Default when omitted:** `false`
   */
  noWarn?: boolean
}

Here's an example of an element definition with no decorators, with HTML attributes mapped to same-name JS properties:

import {Element, element} from '@lume/element'

element(
  class CoolElement extends Element {
    static elementName = 'cool-element'

    static observedAttributeHandlers = {
      foo: {from: Number},
      bar: {from: Boolean},
    }

    // Due to the `observedAttributeHandlers` definition, any time the `"foo"` attribute
    // on the element changes, the attribute string value will be converted into a
    // `Number` and assigned to the JS `.foo` property.
    // Not only does `.foo` have an initial value of `123`, but when the element's
    // `"foo"` attribute is removed, `.foo` will be set back to the initial value
    // of `123`.
    foo = 123

    // Due to the `observedAttributeHandlers` definition, any time the `"bar"` attribute
    // on the element changes, the attribute string value will be converted into a
    // `Boolean` and assigned to the JS `.bar` property.
    // Not only does `.bar` have an initial value of `123`, but when the element's
    // `"bar"` attribute is removed, `.bar` will be set back to the initial value
    // of `false`.
    bar = false

    // ...
  },
)

Example on CodePen

@lume/element comes with a set of basic handlers available out of the box, each of which are alternatives to a respective set of included decorators:

import {Element, element, attribute} from '@lume/element'

element(
  class CoolElement extends Element {
    static elementName = 'cool-element'

    static observedAttributeHandlers = {
      lorem: {}, // Effectively the same as attribute.string
      foo: attribute.string, // Effectively the same as the @stringAttribute decorator. Values get passed to the JS property as strings.
      bar: attribute.number, // Effectively the same as the @numberAttribute decorator. Values get passed to the JS property as numbers.
      baz: attribute.boolean, // Effectively the same as the @booleanAttribute decorator. Values get passed to the JS property as booleans.

      // Here we define an attribute with custom handling of the string value, in this case making it accept a JSON string that maps it to a parsed object on the JS property.
      bespoke: {from: value => JSON.parse(value)}, // f.e. besoke='{"b": true}' results in the JS property having the value `{b: true}`
    }

    // The initial values of the JS properties define the values that the JS properties get reset back to when the corresponding attributes are removed.
    lorem = 'hello'
    foo = 'world'
    bar = 123
    baz = false
    bespoke = {n: 123}

    // ...
  },
)

Example on CodePen

If decorator support is present (either with a build, or natively in near-future JS engines), defining attributes with decorators is simpler and more concise:

import {Element, element, numberAttribute, booleanAttribute} from '@lume/element'

@element
class CoolElement extends Element {
  static elementName = 'cool-element'

  // Due to the `@numberAttribute` decorator, any time the `"foo"` attribute
  // on the element changes, the attribute string value will be converted into a
  // `Number` and assigned to the JS `.foo` property.
  // Not only does `.foo` have an initial value of `123`, but when the element's
  // `"foo"` attribute is removed, `.foo` will be set back to the initial value
  // of `123`.
  @numberAttribute foo = 123

  // Due to the `@booleanAttribute` decorator, any time the `"bar"` attribute
  // on the element changes, the attribute string value will be converted into a
  // `Boolean` and assigned to the JS `.bar` property.
  // Not only does `.bar` have an initial value of `true`, but when the element's
  // `"bar"` attribute is removed, `.bar` will be set back to the initial value
  // of `true`.
  @booleanAttribute bar = true

  // ...
}

Note

Not only do decorators make the definition more concise, but they avoid surface area for human error: the non-decorator form requires defining the same-name property in both the static observedAttributeHandlers object and in the class fields, and if we miss one or the other then things might not work as expected.

Each of the available decorators are detailed further below.

Decorators, and the static observedAttributeHandlers object format, both work with getter/setter properties as well:

import {Element, element, numberAttribute, booleanAttribute} from '@lume/element'

@element // The 'cool-element' name is implied from the constructor name (dash-cased)
class CoolElement extends Element {
  #foo = 123

  // Like with class fields, the initial value is 123, so when the "foo"
  // attribute is removed the setter will receive 123.
  @numberAttribute
  get foo() {
    return this.#foo
  }
  set foo(v) {
    this.#foo = v
  }
  // ...
}

They also work with "auto accessors", which creates a prototype getter/setter:

@element
class CoolElement extends Element {
  // The same rules with initial values and attribute removal apply.
  @numberAttribute accessor foo = 123
  @booleanAttribute accessor bar = false

  // ...
}

It may be redundant to write accessor repeatedly for each property when the alternative non-accessor format works too. The accessor format can be a fallback in very rare cases where a performance boost is needed (for example thousands of objects with many non-accessor properties being instantiated all at once). Most likely there will be other performance issues at the point in which we have thousands of elements being instantiated at once causing an any issues.

events with `static observedAttributeHandlers`

This is an alternative for the @eventAttribute decorator (recommended, see the @eventAttribute docs below), and will be removed after native support for decorators lands in JS engines.

import {Element, element, attribute} from '@lume/element'

const SomeEl = element('some-el')(
  class extends Element {
    static observedAttributeHandlers = {
      onjump: attribute.event,
    }

    // Also define the property explicitly (here with an optional type definition).
    /** @type {EventListener | null} */
    onjump = null

    connectedCallback() {
      super.connectedCallback()

      // This element dispatches a "jump" event every second:
      setInterval(() => this.dispatchEvent(new Event('jump')), 1000)
    }
  },
)

const el = new SomeEl()

el.onjump = () => console.log('jump!')
// or, as with "onclick" and other built-in attributes:
el.setAttribute('onjump', "console.log('jump!')")

document.body.append(el)

// "jump!" will be logged every second.

Note that for TypeScript JSX types (TSX), we want to also define event properties on the class, for example onjump in the last example. Any properties that start with on will be mapped to on-prefixed JSX props for type checking. See the TypeScript section for more info.

`attributeChangedCallback`

Nothing new here, this is simply a part of the browser's native Custom Elements attributeChangedCallback API. It is triggered when an observed attribute of the element is added, modified, or removed.

Note

If you're using Lume Elements's features only, you do not need to define this method. Lume Element's reactive properties will automatically receive updated values when attributes change, and the element's template will automatically update. Writing an attributesChanged callback is only useful if you need to handle something custom that is not covered by Lume Element, for example a 3rd-party lib such as a mixin that implements logic in attributeChangedCallback that needs to be overriden.

import {Element} from '@lume/element'

class CoolElement extends Element {
  static observedAttributes = ['foo', 'bar']

  attributeChangedCallback(attributeName, oldValue, newValue) {
    // Don't forget to call the super method from the Element class!
    super.attributeChangedCallback(attributeName, oldValue, newValue)

    // Attribute name is the name of the attribute change changed.
    // If `oldValue` is `null` and `newValue` is a string, it means the attribute was added.
    // If `oldValue` and `newValue` are both strings, it means the value changed.
    // If `oldValue` is a string and `newValue` is `null`, it means the attribute was removed.
  }
  // ...
}

Warning

The static observedAttributes property is required for observing attributes, and specifies which attributes will trigger attributeChangedCallback. attributeChangedCallback will not be triggered for any attributes that are not listed in static observedAttributes!

`connectedCallback`

Nothing new here, this is simply a part of the browser's native Custom Elements connectedCallback API. It is triggered when the element is connected into the document. Use it to create initialize any processes.

With Lume Element, the main use case of this is to create effects when not using decorator-style effects.

import {Element} from '@lume/element'

class CoolElement extends Element {
  connectedCallback() {
    // Don't forget to call the super method from the Element class!
    super.connectedCallback()

    // ...Create processes, such as effects...

    this.createEffect(() => {
      // ... re-runs when any properties or signals change ...
    })
  }
  // ...
}

When using decorators, the following is preferred for less boilerplate:

import {Element} from '@lume/element'

class CoolElement extends Element {
  // Use the method name to describe the effect for readability.
  @effect someEffect() {
    // ... re-runs when any signals change ...
  }

  connectedCallback() {
    super.connectedCallback() // Don't forget to call the base-class method!

    // ...Create processes (non-effects)...
  }
  // ...
}

`disconnectedCallback`

Nothing new here, this is simply a part of the browser's native Custom Elements disconnectedCallback API. It is triggered when the element is disconnected from the document. Use it to clean things up.

![Note] When using only effects, it is unnecessary to define disconnectedCallback. This example shows how to clean up custom processes.

import {Element} from '@lume/element'
import {effect} from 'classy-solid'

class CoolElement extends Element {
  @effect someEffect() {
    // ...
  }

  connectedCallback() {
    super.connectedCallback() // Don't forget to call the base-class method!

    this.interval = setInterval(() => {...}, 1000)
  }

  disconnectedCallback() {
    super.disconnectedCallback() // Don't forget to call the base-class method!

    // ...Clean up anything that is not Lume-Element-specific...
    clearInterval(this.interval)

    // You do not need to manually clean up effects made with `this.createEffect()`.
  }

  // ...
}

`adoptedCallback`

Nothing new here, this is simply a part of the browser's native Custom Elements adoptedCallback API. It is triggered when the element is adopted into a new document (f.e. in an iframe). You almost never need this.

import {Element} from '@lume/element'

class CoolElement extends Element {
  adoptedCallback() {
    super.adoptedCallback() // Don't forget to call the base-class method!

    // ...Do something when the element was transferred into another window's or iframe's document...
  }
  // ...
}

`createEffect` (prefer `@effect` decorator instead)

The createEffect method is a wrapper around Solid's createEffect with some differences for convenience and when not using decorators:

createRoot is not required in order to dispose of effects created with this.createEffect()
Effects created with this.createEffect() will automatically be cleaned up when the element is disconnected.
Besides being useful for re-running logic on signals changes, this.createEffect() is useful as an alternative to disconnectedCallback when paired with Solid's onCleanup.

Note

When using decorators, use the @effect decorator instead, for conciseness (see concise decorator example further below).

import {Element} from '@lume/element'
import {createSignal, onCleanup} from 'solid-js'

const [count, setCount] = createSignal(0)

setInterval(() => setCount(n => ++n), 1000)

class CoolElement extends Element {
  connectedCallback() {
    super.connectedCallback()

    // Log `count()` any time it changes.
    this.createEffect(() => console.log(count()))

    this.createEffect(() => {
      const interval1 = setInterval(() => console.log('interval 1'), 1000)
      onCleanup(() => clearInterval(interval1))

      const interval2 = setInterval(() => console.log('interval 2'), 1000)
      onCleanup(() => clearInterval(interval2))
    })
  }

  // disconnectedCallback is not required here for effects to clean up on disconnect.
  // Prefer createEffect+onCleanup over disconnectedCallback for composable logic.
}

customElements.define('cool-element', CoolElement)

// After removing the element, onCleanup fires and cleans up the intervals created in connectedCallback (not the count interval outside the element)
setTimeout(() => {
  const el = document.querySelector('cool-element')
  el.remove()
}, 2000)

Example on CodePen

Compare that to using disconnectedCallback:

import {Element} from '@lume/element'
import {createSignal, onCleanup} from 'solid-js'

const [count, setCount] = createSignal(0)

setInterval(() => setCount(n => ++n), 1000)

class CoolElement extends Element {
  #interval1 = 0
  #interval2 = 0

  connectedCallback() {
    super.connectedCallback()

    // Log `count()` any time it changes.
    this.createEffect(() => console.log(count()))

    this.#interval1 = setInterval(() => console.log('interval 1'), 1000)
    this.#interval2 = setInterval(() => console.log('interval 2'), 1000)
  }

  disconnectedCallback() {
    super.disconnectedCallback()

    clearInterval(this.#interval1)
    clearInterval(this.#interval2)
  }
}

customElements.define('cool-element', CoolElement)

Here's what the more concise example looks like with decorators.

import {Element} from '@lume/element'
import {createSignal, onCleanup} from 'solid-js'
import {effect} from 'classy-solid'

const [count, setCount] = createSignal(0)

setInterval(() => setCount(n => ++n), 1000)

class CoolElement extends Element {
  @effect logCount() {
    console.log(count())
  }

  // This effect does not re-run on signal changes, but is useful for setup+cleanup.
  @effect makeIntervals() {
    const interval1 = setInterval(() => console.log('interval 1'), 1000)
    onCleanup(() => clearInterval(interval1))

    const interval2 = setInterval(() => console.log('interval 2'), 1000)
    onCleanup(() => clearInterval(interval2))
  }
}

customElements.define('cool-element', CoolElement)

// After removing the element, onCleanup fires and cleans up the intervals created in connectedCallback (not the count interval outside the element)
setTimeout(() => {
  const el = document.querySelector('cool-element')
  el.remove()
}, 2000)

💡Tip:

Prefer onCleanup instead of disconnectedCallback because composition of logic will be easier while also keeping it co-located and easier to read. That example is simple, but when logic grows, having to clean things up in disconnectedCallback can get more complicated, especially when each piece of creation logic and cleanup logic is multiple lines long and interleaving them would be harder to read. Plus, putting them in effects makes them creatable+cleanable if signals in the effects change, not just if the element is connected or disconnected. For example, the following element cleans up the interval any time the signal changes, not only on disconnect:

import {Element} from '@lume/element'
import {createSignal, onCleanup} from 'solid-js'
import {effect} from 'classy-solid'

const [count, setCount] = createSignal(0)

setInterval(() => setCount(n => ++n), 1000)

class CoolElement extends Element {
  @effect logCount() {
    console.log(count())
  }

  @effect conditionalInterval() {
    // Run the interval only during moments that count() is an even number.
    // Whenever count() is odd, the running interval will be cleaned up and a new interval will not be created.
    // Also, when the element is disconnected (while count() is even), the interval will be cleaned up.
    if (count() % 2 !== 0) return
    const interval = setInterval(() => console.log('interval'), 100)
    onCleanup(() => clearInterval(interval))
  }
}

customElements.define('cool-element', CoolElement)

// After removing the element, onCleanup fires and cleans up any interval
// currently created within the element (not the count interval outside the
// element)
setTimeout(() => {
  const el = document.querySelector('cool-element')
  el.remove()
}, 2500)

Example on CodePen (without decorators)

The beauty of this is we can write logic based on signals, without worrying about disconnectedCallback, and we'll rest assured things clean up properly. Cleanup logic is co-located with the pieces they are relevant to, which opens the door to powerful compositional patterns...

`static autoDefine`

Set this to false to tell the @element decorator (or element() when called as a function) to not automatically define the element in the global customElements registry. When un-specified, it defaults to true.

@element
class SomeEl extends LumeElement<

element

@lume/element

`npm install @lume/element`

Live demos

Table of contents

Cliché Click Counter Example

Intro

Install and Setup

CDN method (easiest, no compiler or command line needed)

Local install with build

Basic Usage

Create custom elements

Easily create and manipulate DOM

Create functional components

Using functional components inside custom elements

Functional components vs custom elements

API

`Element`

`static elementName`

`template`

`static css`

`css`

`static observedAttributes`

`static observedAttributeHandlers`

events with `static observedAttributeHandlers`

`attributeChangedCallback`

`connectedCallback`

`disconnectedCallback`

`adoptedCallback`

`createEffect` (prefer `@effect` decorator instead)

`static autoDefine`

dont-track-me-google

meine

glsl330-cornellbox

Voksel

element

@lume/element

npm install @lume/element

Live demos

Table of contents

Cliché Click Counter Example

Intro

Install and Setup

CDN method (easiest, no compiler or command line needed)

Local install with build

Basic Usage

Create custom elements

Easily create and manipulate DOM

Create functional components

Using functional components inside custom elements

Functional components vs custom elements

API

Element

static elementName

template

static css

css

static observedAttributes

static observedAttributeHandlers

events with static observedAttributeHandlers

attributeChangedCallback

connectedCallback

disconnectedCallback

adoptedCallback

createEffect (prefer @effect decorator instead)

static autoDefine

dont-track-me-google

meine

glsl330-cornellbox

Voksel

search

`npm install @lume/element`

`Element`

`static elementName`

`template`

`static css`

`css`

`static observedAttributes`

`static observedAttributeHandlers`

events with `static observedAttributeHandlers`

`attributeChangedCallback`

`connectedCallback`

`disconnectedCallback`

`adoptedCallback`

`createEffect` (prefer `@effect` decorator instead)

`static autoDefine`