Not in this case, because copying data to and from a web-worker uses "Structured Copy" which is about as fast as JSON unmarshaling, but in this case it's actual

Not in this case, because copying data to and from a web-worker uses "Structured Copy" which is about as fast as JSON unmarshaling, but in this case it's actually doing significantly more work: * read request * parse from JSON to an object * read the data from the object in the worker to the main thread * create a new object in the main thread with the data from the worker Those last 2 steps are about as slow as a JSON.stringify and JSON.parse, and are completely unnecessary. As others have said, adding some filtering to the example makes this example worlds better.