<!DOCTYPE html>
    <html>
        <head>
            <title>Web Worker postMessage example</title>
        </head>
        <body>
            <script>
            const worker = new Worker( 'worker.js' );
        
            worker.addEventListener( 'mycustomevent', console.log );
            
            const event = new CustomEvent( 'mycustomevent' );
            worker.dispatchEvent( event );
            </script>
        </body>
    </html>
self.addEventListener( 'mycustomevent', console.log );