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<!DOCTYPE html>
  <html>
    <head>
      <title>Web Worker postMessage example</title>
    </head>
    <body>
      <script>
      const worker = new Worker( 'worker.js' );
      
      worker.addEventListener( 'message', ( { data } ) => {
        console.log( 'main thread', data );
      } );

      worker.postMessage( 'myData' );
      </script>
    </body>
  
  </html>

self.addEventListener( 'message', ( { data, source } ) => {
  console.log( 'worker thread', data );
    
  self.postMessage( `${ data } – worker processed` );
} );