#concurrency

Master async programming. Patterns: 1. async/await for readability. 2. Promise.all for parallel execution. 3. Promise.allSettled for all results. 4. Promise.race for timeout handling. 5. Try/catch for error handling. 6. Avoid callback hell. 7. Handle unhandled rejections. 8. Sequential vs parallel trade-offs. Use for I/O operations. Don't block event loop. Implement retry logic for resilience.

I am a Python developer learning Go. Explain the concept of "goroutines" and "channels". How do they compare to Python's threading or asyncio? Provide a simple code example in Go that demonstrates concurrent execution using goroutines and channels.

I have a computationally expensive task in my web app that is blocking the main UI thread. Show me how to offload this task to a Web Worker. Provide the code for the main script that creates the worker and the code for the worker script itself (`worker.js`) that performs the calculation and sends the result back.