Node.js Fixes

10 troubleshooting guides — each with the error, why it happens, and copy-paste commands to fix it.

• npm ERR! code ENOTFOUND / network — Registry Failures in CI — npm couldn't reach the registry (ENOTFOUND, ECONNREFUSED, ETIMEDOUT) or the request failed mid-transfer (EINTEGRITY after corrupt cache).
• ECONNRESET in Node.js: Sockets Closed Under You — ECONNRESET means the other end (or a middlebox) closed the TCP connection abruptly.
• Node.js 'JavaScript heap out of memory' (FATAL ERR) — V8 caps the heap (~4GB on 64-bit, less by default in some builds).
• npm ERR! code ELIFECYCLE — The Script Failed, npm Is Just the Messenger — ELIFECYCLE means a package.
• Node.js "EADDRINUSE: address already in use" — Find and Free the Port — Something already listens on that port — usually a previous instance of your own dev server that never died.
• Node.js "Cannot find module" — Path, Deps, or Case Sensitivity — Three different problems share one message: a missing dependency, a relative path typo, or a case-sensitivity mismatch that works on macOS/Windows and fails on Linux.
• Node.js "ERR_REQUIRE_ESM" — require() Against an ESM-Only Package — The package you required ships only ES modules; require() can't load it.
• npm ERR! code EACCES — Cache and Prefix Permission Wars — npm tried to write ~/.
• Node.js "ERR_OSSL_EVP_UNSUPPORTED" — Old Crypto in New Node (Webpack Classic) — Node 17+ ships OpenSSL 3, which removed the legacy MD4 hash webpack (and some older tooling) uses.
• npm ERR! ERESOLVE: Peer Dependency Conflict — Two packages demand incompatible versions of a shared peer (React 17 vs 18 is the classic).