Can the PaintWorklet be inlined?

Question

The idiomatic way to use the CSS Paint API seems to be:

1. Create a xyz.js file
   • Populate with a class containing a paint(ctx, geom, properties) function
   • Call registerPaint, passing the class as an argument
2. Call CSS.paintWorklet.addModule('xyz.js') from your index.html
3. Apply the paint worklet in CSS like background-image: paint(myPaintWorklet);

More details on that here: https://developers.google.com/web/updates/2018/01/paintapi

But having to load a separate .js file is a performance hit.

Is there a way to inline the PaintWorklet so that a separate .js file is not needed?

Answer 1

One way to do it is using Data URLs. Demo: (works for me atleast on chrome 73). Example taken from here

<style>
  textarea {
    background-image: paint(checkerboard);
  }
</style>
<textarea></textarea>
<script>
  CSS.paintWorklet.addModule(`data:application/javascript;charset=utf8,${encodeURIComponent(`
    // checkerboard.js
    class CheckerboardPainter {
      paint(ctx, geom, properties) {
        // Use "ctx" as if it was a normal canvas
        const colors = ['red', 'green', 'blue'];
        const size = 32;
        for(let y = 0; y < geom.height/size; y++) {
          for(let x = 0; x < geom.width/size; x++) {
            const color = colors[(x + y) % colors.length];
            ctx.beginPath();
            ctx.fillStyle = color;
            ctx.rect(x * size, y * size, size, size);
            ctx.fill();
          }
        }
      }
    }
  
    // Register our class under a specific name
    registerPaint('checkerboard', CheckerboardPainter);
  `)}`)
</script>

Another method would be to make a Blob and pass the blob URL to the addModule function. This looks less hackish. Demo:

<style>
  textarea {
    background-image: paint(checkerboard);
  }
</style>
<textarea></textarea>
<script>
  CSS.paintWorklet.addModule(URL.createObjectURL(new Blob([`
    // checkerboard.js
    class CheckerboardPainter {
      paint(ctx, geom, properties) {
        // Use "ctx" as if it was a normal canvas
        const colors = ['red', 'green', 'blue'];
        const size = 32;
        for(let y = 0; y < geom.height/size; y++) {
          for(let x = 0; x < geom.width/size; x++) {
            const color = colors[(x + y) % colors.length];
            ctx.beginPath();
            ctx.fillStyle = color;
            ctx.rect(x * size, y * size, size, size);
            ctx.fill();
          }
        }
      }
    }
  
    // Register our class under a specific name
    registerPaint('checkerboard', CheckerboardPainter);
  `], {type: "application/javascript"})))
</script>