Enhance SSR

Server side render for Custom Elements.

Enhance enables a web standards based workflow that embraces the platform by supporting Custom Elements and slot syntax.

Install

npm i @enhance/ssr

Usage

import HelloWorld from './path/to/elements/hello-world.mjs'
import enhance from '@enhance/ssr'
const html = enhance({
  elements: {
    'hello-world': HelloWorld
  }
})
console.log(html`<hello-world greeting="Well hi!"></hello-world>`)

An example custom element template for use in Server Side Rendering

Elements are pure functions that are passed an object containing an html function used to expand custom elements and a state object comprised of attrs which are the attributes set on the custom element and a store object that contains application state.

export default function HelloWorld({ html, state }) {
  const { attrs } = state
  const { greeting='Hello World' } = attrs
  return html`
    <style scope="global">
      h1 {
        color: red;
      }
    </style>

    <h1>${greeting}</h1>
  `
}

The rendered output

<head>
  <style scope="global">
    h1 {
      color: red;
    }
  </style>
</head>

<body>
<hello-world>
  <h1>Hello World</h1>
</hello-world>
</body>

Render function

You can also use an object that exposes a render function as your template. The render function will be passed the same arguments { html:function, state:object }.

{
  attrs: [ 'label' ],
  init(el) {
    el.addEventListener('click', el.click)
  },
  render({ html, state }) {
    const { attrs={} } = state
    const { label='Nope' } = attrs
    return html`
    <pre>
      ${JSON.stringify(state)}
    </pre>
    <button>${ label }</button>
    `
  },
  click(e) {
    console.log('CLICKED')
  },
  adopted() {
    console.log('ADOPTED')
  },
  connected() {
    console.log('CONNECTED')
  },
  disconnected() {
    console.log('DISCONNECTED')
  }
}

Use these options objects with the enhance custom element factory

Store

Supply initital state to enhance and it will be passed along in a store object nested inside the state object.

Node

import MyStoreData from './path/to/elements/my-store-data.mjs'
import enhance from '@enhance/ssr'
const html = enhance({
  elements: {
    'my-store-data': MyStoreData
  },
  initialState: { apps: [ { users: [ { name: 'tim', id: 001 }, { name: 'kim', id: 002 } ] } ] }
})
console.log(html`<my-store-data app-index="0" user-index="1"></my-store-data>`)

Element template

export default function MyStoreData({ html, state }) {
  const { attrs, store } = state
  const appIndex = attrs['app-index']
  const userIndex = attrs['user-index']
  const { id='', name='' } = store?.apps?.[appIndex]?.users?.[userIndex] || {}
  return `
<div>
  <h1>${name}</h1>
  <h1>${id}</h1>
</div>
  `
}

The store is used to pass state to all components in the tree.

Slots

Enhance supports the use of slots in your custom element templates.

export default function MyParagraph({ html }) {
  return html`
<p>
  <slot name="my-text">
    My default text
  </slot>
</p>
  `
}

You can override the default text by adding a slot attribute with a value that matches the slot name you want to replace.

<my-paragraph>
  <span slot="my-text">Let's have some different text!</span>
</my-paragraph>

Unnamed slots

Enhance supports unnamed slots for when you want to create a container element for all non-slotted child nodes.

export default function MyButton({ html }) {
  return html`
<button>
  <slot>Submit</slot>
</button>
  `
}

<my-button></my-button>

<my-button>Save</my-button>

Transforms

Enhance supports the inclusion of script and style transform functions. You add a function to the array of scriptTransforms and/or styleTransforms and are able to transform the contents however you wish, just return your desired output.

import enhance from '@enhance/ssr'

const html = enhance({
  elements: {
    'my-transform-script': MyTransformScript
  },
  scriptTransforms: [
    function({ attrs, raw }) {
      // raw is the raw text from inside the script tag
      // attrs are the attributes from the script tag
      return raw + ' yolo'
    }
  ],
  styleTransforms: [
    function({ attrs, raw }) {
      // raw is the raw text from inside the style tag
      // attrs are the attributes from the style tag
      const { scope } = attrs
      return `
      /* Scope: ${ scope } */
      ${ raw }
      `
    }
  ]
})

function MyTransformScript({ html }) {
  return html`
<style scope="component">
  :host {
    display: block;
  }
</style>
<h1>My Transform Script</h1>
<script type=module>
  class MyTransformScript extends HTMLElement {
    constructor() {
      super()
    }
  }
  customElements.define('my-transform-script', MyTransformScript)
</script>
  `
}

console.log(html`<my-transform-script></my-transform-script>`)

context

There are times you will need to pass state to nested child custom elements. To avoid the tedium of passing attributes through multiple levels of nested elements Enhance SSR supplies a context object to add state to.

Parent sets context

export default function MyContextParent({ html, state }) {
  const { attrs, context } = state
  const { message } = attrs
  context.message = message

  return html`
    <slot></slot>
  `
}

Child retrieves state from parent supplied context

export default function MyContextChild({ html, state }) {
  const { context } = state
  const { message } = context
  return html`
    <span>${ message }</span>
  `
}

Authoring

<my-context-parent message="hmmm">
  <div>
    <span>
      <my-context-child></my-context-child>
    </span>
  </div>
</my-context-parent>

instanceID

When rendering custom elements from a single template there are times where you may need to target a specific instance. The instanceID is passed in the state object.

export default function MyInstanceID({ html, state }) {
  const { instanceID='' } = state

  return html`
<p>${instanceID}</p>
  `
}

bodyContent

Enhance SSR outputs an entire valid HTML page but you can pass bodyContent: true to get just the content of the <body> element. This can be useful for when you want to isolate the HTML output to just the Custom Element(s) you are authoring.

const html = enhance({
  bodyContent: true,
  elements: {
    'my-paragraph': MyParagraph,
  }
})
const output = html`
<my-paragraph></my-paragraph>
  `

Integration with <html>, <head>, and <body> elements

Enhance SSR will intelligently merge its rendered <html>, <head>, and <body> elements with any that you provide to it (unless you choose to use the bodyContent: true option).

For example:

const html = enhance({
  elements: {
    'my-content': MyContent,
  }
})

html`
<!DOCTYPE html>
<html lang="en">
  <head>
    <title>My Website</title>
  </head>
  <body class="foo bar">
    <my-content></my-content>
  </body>
</html>
`

P.S. Enhance works really well with Begin.