Your async tests pass 9 times out of 10 and fail in CI for no reason. The real bug is in how you test time-dependent code. Here is how to replace setTimeout with deterministic clocks, control promise ordering, and eliminate flakiness from every async test in your suite.
Your API is slow, but you cannot explain why. Your APM shows request time, but you need to break it into DNS resolution, TCP connect, TLS handshake, and downstream call durations. The diagnostics_channel module gives you this data with zero application code changes and zero overhead when nobody is listening.
A cache write is missing, a database row is corrupted, a WebSocket state machine is stuck in limbo. These are not flaky infrastructure problems. They are JavaScript race conditions, and they follow predictable patterns. Here is how to spot, reproduce, and fix the five most common async race patterns in Node.js and the browser.
Every time you wrap an error in another error, you bury the original stack trace. Error.cause is the ES2022 feature that preserves the full chain, and it will save you hours of production debugging.
Your SPA works fine in development and then every cross-origin request fails in staging with a cryptic CORS error. Here is what the preflight, the three response headers, and the credential flag actually do under the hood, plus a test harness that lets you verify CORS behavior before you deploy.
A single unhandled promise rejection took down your Node.js server at 2 AM. Here is how to build a global error boundary that catches uncaught exceptions, unhandled rejections, and async failures, logs actionable context, and keeps the process alive or exits cleanly without losing the trail.
Your p99 jumps every few minutes but CPU, memory, and GC look fine. The event loop is being blocked by synchronous work that never shows up in APM. Here is how to measure lag in production, find the culprits, and fix them without guessing.
Production broke after a three-day sprint and two hundred commits. Hunting the culprit by hand is linear and slow. Git bisect turns it into a logarithmic search, and git bisect run automates the entire hunt. Here is the exact workflow, the test script template, and the CI integration that catches regressions before the next standup.
A practical workflow for catching Node.js memory leaks before the OOM killer does: instrument memory, trigger safe heap snapshots, compare retainers, and ship a fix you can verify.
Most devs reach for console.log when they should be using breakpoints, watch expressions, and conditional breakpoints. Here are the techniques that changed how I debug.
Most performance investigations start with “let's add some console.time calls” and end with three days of guessing. Flame graphs are the visualization that takes you from “the API is slow” to “line 142 is the problem” in one capture. Here is how to read one, generate one in Node.js, and the four shapes that tell you what kind of bug you are looking at.