What are Buffers and when do you use them?

JavaScript strings are for text, not arbitrary bytes. Buffers let Node represent binary data without encoding it. Most stream chunks are buffers, and APIs that work with files, sockets, crypto and compression accept or return them.

const fromString = Buffer.from("hello", "utf8");
const safe = Buffer.alloc(8);
const fast = Buffer.allocUnsafe(8);
const slice = fromString.subarray(0, 2);

console.log(fromString.length);
console.log(safe.toString("hex"));
console.log(slice.toString("utf8"));
console.log(slice.buffer === fromString.buffer);

What to watch

• Buffer.alloc zeroes memory; Buffer.allocUnsafe may expose old data, so always fill it
• subarray and slice share memory, while Buffer.from with a copy creates new storage
• Sizes are in bytes, not characters, so multibyte text has a larger length
• Set an encoding when converting to a string, and handle malformed input explicitly
• Buffers are not resizable; allocate the right size or collect chunks into a list

The usual mistake is concatenating buffers in a loop with repeated Buffer.concat calls, which copies the accumulated data every time. Collect chunks in an array and concatenate once, or stream the data instead of holding it.