How do you identify and fix JavaScript runtime performance issues?

// BAD: Long blocking task
function processLargeArray(items) {
  for (let i = 0; i < items.length; i++) {
    heavyComputation(items[i]); // Blocks main thread
  }
}

// GOOD: Chunked processing with yielding
async function processLargeArrayAsync(items, chunkSize = 100) {
  for (let i = 0; i < items.length; i += chunkSize) {
    const chunk = items.slice(i, i + chunkSize);
    chunk.forEach(item => heavyComputation(item));
    
    // Yield to browser - allow event handling, rendering
    await new Promise(resolve => setTimeout(resolve, 0));
  }
}

// Using scheduler.yield() (if available)
async function processWithYield(items) {
  for (const item of items) {
    heavyComputation(item);
    
    // Yield if task is taking too long
    if (scheduler.yield) {
      await scheduler.yield();
    }
  }
}

// Using requestIdleCallback for non-urgent work
function processInBackground(items) {
  let index = 0;
  
  function processChunk(deadline) {
    while (index < items.length && deadline.timeRemaining() > 0) {
      heavyComputation(items[index]);
      index++;
    }
    
    if (index < items.length) {
      requestIdleCallback(processChunk);
    }
  }
  
  requestIdleCallback(processChunk);
}