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console.log('1: start'); setTimeout(function() { console.log('3: async (after 0ms)'); }, 0); console.log('2: end'); // Output order: 1, 2, 3 // Even with 0ms delay, setTimeout is async function slowSync() { const end = Date.now() + 2000; while (Date.now() < end) {} // blocks for 2 seconds! return 'done'; } // console.log(slowSync()); // freezes everything for 2s fetch('https://api.example.com/data') .then(res => res.json()) .then(data => console.log('data received')) .catch(err => console.error(err)); console.log('This runs before fetch completes');
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