What is Chrome browser's event loop mechanism?

Chrome Event Loop Mechanism

Chrome browser's event loop mechanism is the core of JavaScript asynchronous programming. Understanding it is crucial for writing high-performance frontend applications.

Event Loop Components

1. Call Stack

   • Stores function calls
   • Follows LIFO (Last In First Out) principle
   • Synchronous code executes in the call stack

2. Task Queue

   • Macrotask Queue: setTimeout, setInterval, I/O, UI rendering
   • Microtask Queue: Promise.then, MutationObserver, queueMicrotask

3. Web APIs

   • Asynchronous APIs provided by browser
   • DOM operations, timers, network requests, etc.

Execution Order

1. Execute synchronous code (call stack)
2. When call stack is empty, check microtask queue
3. Execute all microtasks
4. Execute one macrotask
5. Repeat steps 2-4

Key Concepts

• Microtasks have higher priority than macrotasks
• Microtask queue is cleared before each macrotask execution
• UI rendering occurs between macrotasks

Practical Application

javascript
console.log('1');

setTimeout(() => {
  console.log('2');
  Promise.resolve().then(() => console.log('3'));
}, 0);

Promise.resolve().then(() => console.log('4'));

console.log('5');

// Output order: 1, 5, 4, 2, 3

Performance Optimization

• Avoid long-running tasks blocking the main thread
• Use microtasks and macrotasks appropriately
• Use requestAnimationFrame for animations
• Avoid heavy computations in microtasks