JavaScript Module Workers: Mastering Background Processing Patterns for a Global Digital Landscape

            
// worker.js

// This function will be executed when the worker receives a message
self.onmessage = function(event) {
  const data = event.data;
  console.log('Message received in worker:', data);

  // Perform some background task
  const result = data.value * 2;

  // Send the result back to the main thread
  self.postMessage({ result: result });
};

console.log('Module Worker initialized.');

            

              
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// main.js

// Check if Module Workers are supported
if (window.Worker) {
  // Create a new Module Worker
  // Note: The path should point to a module file (often with .js extension)
  const myWorker = new Worker('./worker.js', { type: 'module' });

  // Listen for messages from the worker
  myWorker.onmessage = function(event) {
    console.log('Message received from worker:', event.data);
  };

  // Send a message to the worker
  myWorker.postMessage({ value: 10 });

  // You can also handle errors
  myWorker.onerror = function(error) {
    console.error('Worker error:', error);
  };
} else {
  console.log('Your browser does not support Web Workers.');
}

            

              
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// worker.js

let taskQueue = [];
let isProcessing = false;

async function processTask(task) {
  console.log(`Processing task: ${task.type}`);
  // Simulate a computationally intensive operation
  await new Promise(resolve => setTimeout(resolve, task.duration || 1000));
  return `Task ${task.type} completed.`;
}

async function runQueue() {
  if (isProcessing || taskQueue.length === 0) {
    return;
  }

  isProcessing = true;
  const currentTask = taskQueue.shift();

  try {
    const result = await processTask(currentTask);
    self.postMessage({ status: 'success', taskId: currentTask.id, result: result });
  } catch (error) {
    self.postMessage({ status: 'error', taskId: currentTask.id, error: error.message });
  } finally {
    isProcessing = false;
    runQueue(); // Process the next task
  }
}

self.onmessage = function(event) {
  const { type, data, taskId } = event.data;

  if (type === 'addTask') {
    taskQueue.push({ id: taskId, ...data });
    runQueue();
  } else if (type === 'processAll') {
    // Immediately attempt to process any queued tasks
    runQueue();
  }
};

console.log('Task Queue Worker initialized.');

            

              
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// main.js

if (window.Worker) {
  const taskWorker = new Worker('./worker.js', { type: 'module' });
  let taskIdCounter = 0;

  taskWorker.onmessage = function(event) {
    console.log('Worker message:', event.data);
    if (event.data.status === 'success') {
      // Handle successful task completion
      console.log(`Task ${event.data.taskId} finished with result: ${event.data.result}`);
    } else if (event.data.status === 'error') {
      // Handle task errors
      console.error(`Task ${event.data.taskId} failed: ${event.data.error}`);
    }
  };

  function addTaskToWorker(taskData) {
    const taskId = ++taskIdCounter;
    taskWorker.postMessage({ type: 'addTask', data: taskData, taskId: taskId });
    console.log(`Added task ${taskId} to queue.`);
    return taskId;
  }

  // Example usage: Add multiple tasks
  addTaskToWorker({ type: 'image_resize', duration: 1500 });
  addTaskToWorker({ type: 'data_fetch', duration: 2000 });
  addTaskToWorker({ type: 'data_process', duration: 1200 });

  // Optionally trigger processing if needed (e.g., on a button click)
  // taskWorker.postMessage({ type: 'processAll' });

} else {
  console.log('Web Workers are not supported in this browser.');
}

            

              
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// data-analyzer.js

export function aggregateData(data) {
  console.log('Aggregating data in worker...');
  // Simulate complex aggregation
  let sum = 0;
  for (let i = 0; i < data.length; i++) {
    sum += data[i];
    // Introduce a small delay to simulate computation
    // In a real scenario, this would be actual computation
    for(let j = 0; j < 1000; j++) { /* delay */ }
  }
  return { total: sum, count: data.length };
}

            

              
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// analyticsWorker.js

import { aggregateData } from './data-analyzer.js';

self.onmessage = function(event) {
  const { dataset } = event.data;
  if (!dataset) {
    self.postMessage({ status: 'error', message: 'No dataset provided' });
    return;
  }

  try {
    const result = aggregateData(dataset);
    self.postMessage({ status: 'success', result: result });
  } catch (error) {
    self.postMessage({ status: 'error', message: error.message });
  }
};

console.log('Analytics Worker initialized.');

            

              
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// main.js

if (window.Worker) {
  const analyticsWorker = new Worker('./analyticsWorker.js', { type: 'module' });

  analyticsWorker.onmessage = function(event) {
    console.log('Analytics result:', event.data);
    if (event.data.status === 'success') {
      document.getElementById('results').innerText = `Total: ${event.data.result.total}, Count: ${event.data.result.count}`;
    } else {
      document.getElementById('results').innerText = `Error: ${event.data.message}`;
    }
  };

  // Prepare a large dataset (simulated)
  const largeDataset = Array.from({ length: 10000 }, (_, i) => i + 1);

  // Send data to the worker for processing
  analyticsWorker.postMessage({ dataset: largeDataset });

} else {
  console.log('Web Workers are not supported.');
}

            

              
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<div id="results">Processing data...</div>

            

              
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// cacheWorker.js

let cache = {};
let websocket = null;

function setupWebSocket() {
  // Replace with your actual WebSocket endpoint
  const wsUrl = 'wss://your-realtime-api.example.com/data';
  websocket = new WebSocket(wsUrl);

  websocket.onopen = () => {
    console.log('WebSocket connected.');
    // Request initial data or subscription
    websocket.send(JSON.stringify({ action: 'subscribe', topic: 'updates' }));
  };

  websocket.onmessage = (event) => {
    try {
      const message = JSON.parse(event.data);
      console.log('Received WS message:', message);
      if (message.type === 'update') {
        cache[message.key] = message.value;
        // Notify main thread about the updated cache
        self.postMessage({ type: 'cache_update', key: message.key, value: message.value });
      }
    } catch (e) {
      console.error('Failed to parse WebSocket message:', e);
    }
  };

  websocket.onerror = (error) => {
    console.error('WebSocket error:', error);
    // Attempt to reconnect after a delay
    setTimeout(setupWebSocket, 5000);
  };

  websocket.onclose = () => {
    console.log('WebSocket disconnected. Reconnecting...');
    setTimeout(setupWebSocket, 5000);
  };
}

self.onmessage = function(event) {
  const { type, data, key } = event.data;

  if (type === 'init') {
    // Potentially fetch initial data from an API if WS is not ready
    // For simplicity, we rely on WS here.
    setupWebSocket();
  } else if (type === 'get') {
    const cachedValue = cache[key];
    self.postMessage({ type: 'cache_response', key: key, value: cachedValue });
  } else if (type === 'set') {
    cache[key] = data;
    self.postMessage({ type: 'cache_update', key: key, value: data });
    // Optionally, send updates to the server if needed
    if (websocket && websocket.readyState === WebSocket.OPEN) {
      websocket.send(JSON.stringify({ action: 'update', key: key, value: data }));
    }
  }
};

console.log('Cache Worker initialized.');

// Optional: Add cleanup logic if the worker is terminated
self.onclose = () => {
  if (websocket) {
    websocket.close();
  }
};

            

              
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// main.js

if (window.Worker) {
  const cacheWorker = new Worker('./cacheWorker.js', { type: 'module' });

  cacheWorker.onmessage = function(event) {
    console.log('Cache worker message:', event.data);
    if (event.data.type === 'cache_update') {
      console.log(`Cache updated for key: ${event.data.key}`);
      // Update UI elements if necessary
    }
  };

  // Initialize the worker and WebSocket connection
  cacheWorker.postMessage({ type: 'init' });

  // Later, request cached data
  setTimeout(() => {
    cacheWorker.postMessage({ type: 'get', key: 'userProfile' });
  }, 3000); // Wait a bit for initial data sync

  // To set a value
  setTimeout(() => {
    cacheWorker.postMessage({ type: 'set', key: 'userSettings', data: { theme: 'dark' } });
  }, 5000);

} else {
  console.log('Web Workers are not supported.');
}

            

              
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// imageProcessorWorker.js

let imageProcessorModule = null;

async function initializeWasm() {
  try {
    // Dynamically import the Wasm module
    // The path './image_processor.wasm' needs to be accessible.
    // You might need to configure your build tool to handle Wasm imports.
    const response = await fetch('./image_processor.wasm');
    const buffer = await response.arrayBuffer();
    const module = await WebAssembly.instantiate(buffer, {
      // Import any necessary host functions or modules here
      env: {
        log: (value) => console.log('Wasm Log:', value),
        // Example: Pass a function from worker to Wasm
        // This is complex, often data is passed via shared memory (ArrayBuffer)
      }
    });
    imageProcessorModule = module.instance.exports;
    console.log('WebAssembly module loaded and instantiated.');
    self.postMessage({ status: 'wasm_ready' });
  } catch (error) {
    console.error('Error loading or instantiating Wasm:', error);
    self.postMessage({ status: 'wasm_error', message: error.message });
  }
}

self.onmessage = async function(event) {
  const { type, imageData, width, height } = event.data;

  if (type === 'process_image') {
    if (!imageProcessorModule) {
      self.postMessage({ status: 'error', message: 'Wasm module not ready.' });
      return;
    }

    try {
      // Assuming Wasm function expects a pointer to image data and dimensions
      // This requires careful memory management with Wasm.
      // A common pattern is to allocate memory in Wasm, copy data, process, then copy back.

      // For simplicity, let's assume imageProcessorModule.process receives raw image bytes
      // and returns processed bytes.
      // In a real scenario, you'd use SharedArrayBuffer or pass ArrayBuffer.

      const processedImageData = imageProcessorModule.process(imageData, width, height);

      self.postMessage({ status: 'success', processedImageData: processedImageData });
    } catch (error) {
      console.error('Wasm image processing error:', error);
      self.postMessage({ status: 'error', message: error.message });
    }
  }
};

// Initialize Wasm when the worker starts
initializeWasm();

            

              
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// main.js

if (window.Worker) {
  const imageWorker = new Worker('./imageProcessorWorker.js', { type: 'module' });
  let isWasmReady = false;

  imageWorker.onmessage = function(event) {
    console.log('Image worker message:', event.data);
    if (event.data.status === 'wasm_ready') {
      isWasmReady = true;
      console.log('Image processing is ready.');
      // Now you can send images for processing
    } else if (event.data.status === 'success') {
      console.log('Image processed successfully.');
      // Display the processed image (event.data.processedImageData)
    } else if (event.data.status === 'error') {
      console.error('Image processing failed:', event.data.message);
    }
  };

  // Example: Assuming you have an image file to process
  // Fetch the image data (e.g., as an ArrayBuffer)
  fetch('./sample_image.png')
    .then(response => response.arrayBuffer())
    .then(arrayBuffer => {
      // You would typically extract image data, width, height here
      // For this example, let's simulate data
      const dummyImageData = new Uint8Array(1000);
      const imageWidth = 10;
      const imageHeight = 10;

      // Wait until Wasm module is ready before sending data
      const sendImage = () => {
        if (isWasmReady) {
          imageWorker.postMessage({
            type: 'process_image',
            imageData: dummyImageData, // Pass as ArrayBuffer or Uint8Array
            width: imageWidth,
            height: imageHeight
          });
        } else {
          setTimeout(sendImage, 100);
        }
      };
      sendImage();
    })
    .catch(error => {
      console.error('Error fetching image:', error);
    });

} else {
  console.log('Web Workers are not supported.');
}

            

              
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// workerPool.js

// Simulate a task that takes time
function performComplexCalculation(input) {
  let result = 0;
  for (let i = 0; i < 1e7; i++) {
    result += Math.sin(input * i) * Math.cos(input / i);
  }
  return result;
}

self.onmessage = function(event) {
  const { taskInput, taskId } = event.data;
  console.log(`Worker ${self.name || ''} processing task ${taskId}`);
  try {
    const result = performComplexCalculation(taskInput);
    self.postMessage({ status: 'success', result: result, taskId: taskId });
  } catch (error) {
    self.postMessage({ status: 'error', error: error.message, taskId: taskId });
  }
};

console.log('Worker pool member initialized.');

            

              
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// main.js

const MAX_WORKERS = navigator.hardwareConcurrency || 4; // Use available cores, default to 4
let workers = [];
let taskQueue = [];
let availableWorkers = [];

function initializeWorkerPool() {
  for (let i = 0; i < MAX_WORKERS; i++) {
    const worker = new Worker('./workerPool.js', { type: 'module' });
    worker.name = `Worker-${i}`;
    worker.isBusy = false;

    worker.onmessage = function(event) {
      console.log(`Message from ${worker.name}:`, event.data);
      if (event.data.status === 'success' || event.data.status === 'error') {
        // Task completed, mark worker as available
        worker.isBusy = false;
        availableWorkers.push(worker);
        // Process next task if any
        processNextTask();
      }
    };

    worker.onerror = function(error) {
      console.error(`Error in ${worker.name}:`, error);
      worker.isBusy = false;
      availableWorkers.push(worker);
      processNextTask(); // Attempt to recover
    };

    workers.push(worker);
    availableWorkers.push(worker);
  }
  console.log(`Worker pool initialized with ${MAX_WORKERS} workers.`);
}

function addTask(taskInput) {
  taskQueue.push({ input: taskInput, id: Date.now() + Math.random() });
  processNextTask();
}

function processNextTask() {
  if (taskQueue.length === 0 || availableWorkers.length === 0) {
    return;
  }

  const worker = availableWorkers.shift();
  const task = taskQueue.shift();

  worker.isBusy = true;
  console.log(`Assigning task ${task.id} to ${worker.name}`);
  worker.postMessage({ taskInput: task.input, taskId: task.id });
}

// Main execution
if (window.Worker) {
  initializeWorkerPool();

  // Add tasks to the pool
  for (let i = 0; i < 20; i++) {
    addTask(i * 0.1);
  }

} else {
  console.log('Web Workers are not supported.');
}

            

              
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