Should I use sync or async file APIs in Node.js?
Always prefer async APIs like fs.readFile in production, so you do not block the event loop. Sync APIs like fs.readFileSync are fine for scripts, build tools, and startup code where blocking does not affect concurrent connections.
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More FAQs in Non-Blocking I/O in Node.js Explained: Why It Matters
A model where the thread initiates an I/O operation, moves on to other work, and processes the result when the operation completes via a callback. Node.js delegates I/O to libuv and processes callbacks through the event loop, so the single thread is not blocked waiting for I/O.
Because web servers handle many concurrent requests. If each request blocks the thread waiting for I/O, the server needs a thread per connection, using more memory. Non-blocking I/O handles thousands of connections on one thread efficiently.
By delegating I/O operations to libuv, which handles them asynchronously. When an operation completes, its callback is queued. The event loop processes these callbacks on the main thread, one at a time, without the thread being blocked.
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