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Explain the JavaScript Event Loop

Answer​

The event loop is how JavaScript handles asynchronous operations despite being single-threaded.

Components​

Execution Order​

  1. Execute synchronous code (call stack)
  2. Process all microtasks (Promises)
  3. Process one macrotask (setTimeout, events)
  4. Repeat

Example​

console.log("1");

setTimeout(() => console.log("2"), 0);

Promise.resolve().then(() => console.log("3"));

console.log("4");

// Output: 1, 4, 3, 2

Key Points​

  • Microtasks run before macrotasks
  • Promise.then() is a microtask
  • setTimeout is a macrotask