Web Worker Communication

When a Web Worker completes its task and posts a message back to the main thread using the postMessage method, the main thread asynchronously receives this message through the worker's onmessage event handler. The main thread does not pause or wait for the Web Worker to finish before continuing its own execution.

Sequence of Events

1. Web Worker Execution:

   • The Web Worker performs its tasks independently in the background, separate from the main thread.

2. Message Posting:

   • When the Web Worker completes its computation or task, it uses the postMessage method to send a message back to the main thread. For example:

     // Inside the Web Worker
     postMessage(result);

3. Main Thread Listening:

   • The main thread, which initiated the Web Worker, has set up an onmessage event listener to handle messages from the worker. For example:

     // Inside the main thread
     worker.onmessage = function(event) {
       const result = event.data;
       // Process the result from the Web Worker
     };

4. Asynchronous Handling:

   • The main thread continues its execution while waiting for the Web Worker's message. When the message is received, the specified event handler (in this case, the onmessage handler) is triggered asynchronously.

5. Handling the Result:

   • The main thread processes the result received from the Web Worker in the event handler.

This asynchronous nature allows the main thread to remain responsive and continue executing other tasks while waiting for the Web Worker to complete its work. It's important to note that the exact timing of when the main thread processes the Web Worker's message depends on the event loop and the current execution context.