Question 1

What is a Buffer in Node.js?

Accepted Answer

A fixed-length sequence of bytes for binary data, backed by outside-V8 memory (historically) / ArrayBuffer views. Used for file, network, and crypto data. Encoding matters when converting to/from strings. Never treat untrusted Buffers as UTF-8 blindly without validation.

Question 2

Buffer.alloc vs Buffer.allocUnsafe vs Buffer.from — security angle?

Accepted Answer

alloc zero-fills; allocUnsafe may contain old memory (leak risk); from copies/interprets input. Never use allocUnsafe for buffers that might be returned to users. Prefer alloc/from. This is a classic security interview question.

Question 3

How do encodings interact with Buffer.toString?

Accepted Answer

toString(encoding) decodes bytes; wrong encoding corrupts data (e.g., binary as utf8). For binary protocols prefer Buffers/Uint8Array end-to-end. Be explicit about utf8 vs base64 vs hex at boundaries.

Question 4

When should you prefer Uint8Array / TypedArrays over Buffer?

Accepted Answer

When writing portable web-compatible code or sharing with Web APIs; Buffer is a Uint8Array subclass in modern Node. Interoperability with fetch, WebCrypto, and isomorphic libs favors typed arrays. Still use Buffer APIs when Node-specific helpers help.

Question 5

Scenario: concatenating many small Buffers in a hot path is slow. Fix?

Accepted Answer

Use Buffer.concat with known length, or a streaming approach / list of chunks with final concat once. Repeated concat allocates repeatedly. Pre-size or stream. Profile before micro-optimizing.

Buffers Node.js Interview Questions

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