swtl

Check out the swtl-starter app

A Service Worker Templating Language (swtl) for component-like templating in service workers. Streams templates to the browser as they're being parsed, and handles rendering iterables/Responses in templates by default.

npm i swtl

Example

import { html, Router, CacheFirst } from 'swtl';
import { BreadCrumbs } from './BreadCrumbs.js'

function HtmlPage({children, title}) {
  return html`<html><head><title>${title}</title></head><body>${children}</body></html>`;
}

function Footer() {
  return html`<footer>Copyright</footer>`;
}

const router = new Router({
  routes: [
    {
      path: '/',
      render: ({params, query, request}) => html`
        <${HtmlPage} title="Home">
          <h1>Home</h1>
          <nav>
            <${BreadCrumbs} path=${request.url.pathname}/>
          </nav>
          ${fetch('./some-partial.html')}
          ${caches.match('./another-partial.html')}
          <ul>
            ${['foo', 'bar', 'baz'].map(i => html`<li>${i}</li>`)}
          </ul>
          <${CacheFirst} file="./some-file.html"/>
          <${Footer}/>
        <//>
      `
    },
  ]
});

self.addEventListener('fetch', (event) => {
  if (event.request.mode === 'navigate') {
    event.respondWith(router.handleRequest(event.request));
  }
});

Router

Uses URLPattern internally for matching the paths. The render callback gets passed the native Request object, as well as any route params or query params.

import { html, Router } from 'swtl';

const router = new Router({
  routes: [
    {
      path: '/',
      render: () => html`<h1>Home</h1>`
    },
    {
      path: '/:foo',
      render: ({params}) => html`<h1>${params.foo}</h1>`
    },
    {
      path: '/:foo/:bar',
      render: ({params}) => html`<h1>${params.foo}/${params.bar}</h1>`
    },
    {
      path: '/:foo/:bar',
      render: ({params, query, request}) => html`<h1>${params.foo}/${params.bar}</h1>`
    },
  ]
});

self.addEventListener('fetch', (event) => {
  if (event.request.mode === 'navigate') {
    event.respondWith(router.handleRequest(event.request));
  }
});

`baseHref`

You can also specify a baseHref, for example if your app is served under a specific base route, like https://my-app.com/foo/bar/:

const router = new Router({
  baseHref: '/foo/bar/',
  routes: [
    {
      // The url will be: https://my-app.com/foo/bar/
      path: '',
      render: () => html`<${Home}/>`
    },
    {
      // The url will be: https://my-app.com/foo/bar/users/1
      path: 'users/:id',
      render: ({params}) => html`<${User} id=${params.id}/>`
    }
  ]
});

Note that you also have the set the base tag in your HTML:

<base href="/foo/bar/">

`fallback`

You can also provide a fallback in case no routes are matched. If you don't provide a fallback, the request will not be handled by the service worker, and go through to the network.

const router = new Router({
  routes: [
    {
      path: '/',
      render: () => html`<${Home}/>`
    }
  ],
  fallback: ({query, request}) => html`<${NotFound}/>`
});

`plugins`

You can also provide plugins. You can add global plugins that will run for every route, or add plugins for specific routes only. If you return a Response from a plugin, the router will return that response to the browser instead of your render function.

import { Router, html, HtmlResponse } from 'swtl';

const logger = {
  name: 'logger-plugin',
  beforeResponse({request}) {
    console.log(`Request made to ${request.url}`);
  }
}

const router = new Router({
  /**
   * These plugins run for all routes
   */
  plugins: [logger],
  routes: [
    {
      path: '/',
      render: () => html`<${Home}/>`,
      /**
       * These plugins run for this route only
       */
      plugins: [
        {
          name: 'my-plugin',
          async beforeResponse({query, params, request}) {
            console.log('Running [my-plugin]!');

            /**
             * Based on conditions we can return a different response
             */
            if (query.foo === 'bar') {
              return new Response('bar');
            }

            if (query.bar === 'foo') {
              /**
               * Returns a `Response` with a stream of the html template as body for convenience
               */
              return new HtmlResponse(html`<${Bar}/>`);
            }

            /**
             * We can also use plugins for redirects
             */
            if (params.user === 'frank') {
              return Response.redirect('/foo');
            }
          }
        }
      ]
    }
  ]
});

Html

Basic usage

/**
 * Children
 */
function Heading({children}) {
  return html`<h1>${children}</h1>`;
}

html`<${Heading}>Hello world<//>`

/**
 * Self-closing
 */
function Heading() {
  return html`<h1>Hello world</h1>`;
}

html`<${Heading}/>`

/**
 * Properties and spread
 */
function MyComponent({foo, title, baz, qux, bool}) {
  return html`
    <h1>${title}</h1>
    <div>${foo}</div>
    <div>${baz} ${qux}</div>
    <div>${bool}</div>
  `;
}

const object = {
  baz: 'hello',
  qux: 'world',
}

html`<${MyComponent} title="hello" foo=${1} ...bar=${object} bool/>`;

/** 
 * Note that quotes are optional when using expressions, the following is also fine:
 * foo="${1}"
 * ...bar="${object}"
 */

Iterables/Responses

You can also use iterables or Responses in your templates directly

const stream = new ReadableStream({
  start(controller) {
    ['a', 'b', 'c'].forEach(s => controller.enqueue(s));
    controller.close();
  }
});

function* gen() {
  yield '<li>1</li>';
  yield '<li>2</li>';
  yield '<li>3</li>';
}

const template = html`
  <main> 
    ${fetch('/some.html')}
    ${caches.match('/some.html')}
    ${new Response('hello')}
    ${stream}
    <ul>
      ${gen()}
    </ul>
  </main>
`;

Strategies

We also ship some built-in components to declaratively let you request files.

import { NetworkFirst, NetworkOnly, CacheFirst, CacheOnly, html } from 'swtl';

const template = html`
  <h1>Hello world</h1>
  
  <${NetworkFirst} file="./some-file.html"/>
  <${NetworkOnly} file="./some-file.html"/>
  <${CacheFirst} file="./some-file.html"/>
  <${CacheOnly} file="./some-file.html"/>

  <footer>Copyright</footer>
`;

You can also provide a fallback:

const template = html`
  <${NetworkFirst} file="./some-file.html">
    <div>Failed to fetch, and not in cache</div>
  <//>

  <${NetworkOnly} file="./some-file.html">
    <div>Failed to fetch</div>
  <//>

  <${CacheFirst} file="./some-file.html">
    <div>Not in cache, and failed to fetch</div>
  <//>

  <${CacheOnly} file="./some-file.html">
    <div>Not in cache</div>
  <//>
`;

Out of order streaming

For out of order streaming you can use the built-in Await component and provide a promise property:

import { Await, when } from 'swtl';

html`
  <${Await} promise=${() => fetch('/api/foo').then(r => r.json())}>
    ${(status, data, error) => html`
      <h1>Fetching data</h1>
      ${when(status.pending, () => html`<p>Loading...</p>`)}
      ${when(status.error, () => html`<p>Failed to fetch data</p>`)}
      ${when(status.success, () => html`
        <ul>
          ${data.map(i => html`<li>${i}</li>`)}
        </ul>
      `)}
    `}
  <//>
`

Render

The Router streams responses to the browser via the render function internally in handleRequest:

import { render } from 'swtl';

for await (const chunk of render(html`<h1>${1}</h1>`)) {
  console.log(chunk);
}

But we also export a renderToString:

import { renderToString } from 'swtl';

const result = await renderToString(html`<h1>${1}</h1>`);

Acknowledgements

Inspired by libraries like preact/htm and lit-html.

And Astro for doing the hard work of implementing the rendering logic back when I requested this to be supported in Astro.

❤️

gryzzly/swtl