Debugging Node with the inspector

Node includes the V8 inspector, the same debugging protocol Chrome uses. Start your program with a flag:

• node --inspect app.js — runs normally and listens for a debugger on 127.0.0.1:9229.
• node --inspect-brk app.js — pauses before the first line, so you can set breakpoints in startup code.
• node --inspect-wait app.js — waits for a debugger to attach, then runs.

Then attach a client:

• Chrome: open chrome://inspect, click "Open dedicated DevTools for Node". You get Sources, breakpoints, the console in your program's context, plus Memory and Performance tabs.
• VS Code: the JavaScript Debug Terminal auto-attaches to any node you start in it, or create a launch configuration. Breakpoints are set in the editor gutter.

Inside the debugger you can step over/into/out, inspect the call stack (including async frames, so you see which await led here), add watch expressions, and set conditional breakpoints or logpoints that print without pausing. A debugger; statement in code acts as a breakpoint when a debugger is attached.

Never expose the inspector on a public interface: --inspect=0.0.0.0 gives anyone who can reach the port full code execution in your process. To debug a remote machine, keep the default localhost binding and use an SSH tunnel.

Other helpful tools: node inspect app.js is a terminal debugger; NODE_DEBUG=http,net turns on internal debug logs of core modules; console.trace() prints the current stack; --enable-source-maps makes stack traces point to TypeScript sources. For tests, node --inspect-brk --test lets you step through a failing test.