Why does slicing a Buffer change the original bytes?

A Buffer view can share the same underlying memory. Editing the view then edits the original allocation rather than an independent copy. Use Buffer.from(view) when independent bytes are required, and test by mutating one side after construction. Distinguish Buffer behavior from assumptions based on ordinary JavaScript arrays. Sharing memory is useful for efficient parsing, but ownership must be clear when data crosses asynchronous boundaries. Do not return a mutable view of secret or reusable scratch storage to unrelated callers. Copying adds memory cost, so copy at the boundary that actually requires isolation. Minimal example:

import assert from 'node:assert/strict';
const original = Buffer.from([1, 2, 3]);
const view = original.subarray(0, 2);
const copy = Buffer.from(view);
view[0] = 9;
assert.equal(original[0], 9);
assert.equal(copy[0], 1);