Hacking Together Our Own import from '#id'

Exports/imports between inline scripts aren’t natively supported, but it was a fun exercise to hack together an implementation for my documents. Code-golfed down to a small block, I use it like this:

<script type="module" data-info="https://stackoverflow.com/a/43834063">let l,e,t="script",p=/(from\s+|import\s+)['"](#[\w\-]+)['"]/g,x='textContent',d=document,
s,o;for(o of d.querySelectorAll(t+'[type=inline-module]'))l=d.createElement(t),o
.id?l.id=o.id:0,l.type="module",l[x]=o[x].replace(p,(u,a,z)=>(e=d.querySelector(
t+z+'[type=module][src]'))?a+`/* ${z} */'${e.src}'`:u),l.src=URL.createObjectURL
(new Blob([l[x]],{type:'application/java'+t})),o.replaceWith(l)//inline</script>

<script type="inline-module" id="utils">
  let n = 1;
  
  export const log = message => {
    const output = document.createElement('pre');
    output.textContent = `[${n++}] ${message}`;
    document.body.appendChild(output);
  };
</script>

<script type="inline-module" id="dogs">
  import {log} from '#utils';
  
  log("Exporting dog names.");
  
  export const names = ["Kayla", "Bentley", "Gilligan"];
</script>

<script type="inline-module">
  import {log} from '#utils';
  import {names as dogNames} from '#dogs';
  
  log(`Imported dog names: ${dogNames.join(", ")}.`);
</script>

Instead of <script type="module">, we need to define our script elements using a custom type like <script type="inline-module">. This prevents the browser from trying to execute their contents itself, leaving them for us to handle. The script (full version below) finds all inline-module script elements in the document, and transforms them into regular script module elements with the behaviour we want.

Inline scripts can’t be directly imported from each other, so we need to give the scripts importable URLs. We generate a blob: URL for each of them, containing their code, and set the src attribute to run from that URL instead of running inline. The blob: URLs acts like normal URLs from the server, so they can be imported from other modules. Each time we see a subsequent inline-module trying to import from '#example', where example is the ID of a inline-module we’ve transformed, we modify that import to import from the blob: URL instead. This maintains the one-time execution and reference deduplication that modules are supposed to have.

<script type="module" id="dogs" src="blob:https://example.com/9dc17f20-04ab-44cd-906e">
  import {log} from /* #utils */ 'blob:https://example.com/88fd6f1e-fdf4-4920-9a3b';

  log("Exporting dog names.");

  export const names = ["Kayla", "Bentley", "Gilligan"];
</script>

The execution of module script elements is always deferred until after the document is parsed, so we don’t need to worry about trying to support the way that traditional script elements can modify the document while it’s still being parsed.

export {};

for (const original of document.querySelectorAll('script[type=inline-module]')) {
  const replacement = document.createElement('script');

  // Preserve the ID so the element can be selected for import.
  if (original.id) {
    replacement.id = original.id;
  }

  replacement.type="module";

  const transformedSource = original.textContent.replace(
    // Find anything that looks like an import from '#some-id'.
    /(from\s+|import\s+)['"](#[\w\-]+)['"]/g,
    (unmodified, action, selector) => {
      // If we can find a suitable script with that id...
      const refEl = document.querySelector('script[type=module][src]' + selector);
      return refEl ?
        // ..then update the import to use that script's src URL instead.
        `${action}/* ${selector} */ '${refEl.src}'` :
        unmodified;
    });

  // Include the updated code in the src attribute as a blob URL that can be re-imported.
  replacement.src = URL.createObjectURL(
    new Blob([transformedSource], {type: 'application/javascript'}));

  // Insert the updated code inline, for debugging (it will be ignored).
  replacement.textContent = transformedSource;

  original.replaceWith(replacement);
}

Warnings: this simple implementation doesn’t handle script elements added after the initial document has been parsed, or allow script elements to import from other script elements that occur after them in the document. If you have both module and inline-module script elements in a document, their relative execution order may not be correct. The source code transformation is performed using a crude regex that won’t handle some edge cases such as periods in IDs.