node:module APInode:module APINode.js includes a command-line debugging utility. The Node.js debugger clientis not a full-featured debugger, but simple stepping and inspection arepossible.
To use it, start Node.js with theinspect argument followed by the path to thescript to debug.
$node inspect myscript.js< Debugger listening on ws://127.0.0.1:9229/621111f9-ffcb-4e82-b718-48a145fa5db8< For help, see: https://nodejs.org/en/docs/inspector<< Debugger attached.< okBreak on start in myscript.js:2 1 // myscript.js>2 global.x = 5; 3 setTimeout(() => { 4 debugger;debug>The debugger automatically breaks on the first executable line. To insteadrun until the first breakpoint (specified by adebugger statement), settheNODE_INSPECT_RESUME_ON_START environment variable to1.
$cat myscript.js// myscript.jsglobal.x = 5;setTimeout(() => { debugger; console.log('world');}, 1000);console.log('hello');$NODE_INSPECT_RESUME_ON_START=1 node inspect myscript.js< Debugger listening on ws://127.0.0.1:9229/f1ed133e-7876-495b-83ae-c32c6fc319c2< For help, see: https://nodejs.org/en/docs/inspector<connecting to 127.0.0.1:9229 ... ok< Debugger attached.<< hello<break in myscript.js:4 2 global.x = 5; 3 setTimeout(() => {>4 debugger; 5 console.log('world'); 6 }, 1000);debug>nextbreak in myscript.js:5 3 setTimeout(() => { 4 debugger;>5 console.log('world'); 6 }, 1000); 7 console.log('hello');debug>replPress Ctrl+C to leave debug repl>x5>2 + 24debug>next< world<break in myscript.js:6 4 debugger; 5 console.log('world');>6 }, 1000); 7 console.log('hello'); 8debug>.exit$Therepl command allows code to be evaluated remotely. Thenext commandsteps to the next line. Typehelp to see what other commands are available.
Pressingenter without typing a command will repeat the previous debuggercommand.
It is possible to watch expression and variable values while debugging. Onevery breakpoint, each expression from the watchers list will be evaluatedin the current context and displayed immediately before the breakpoint'ssource code listing.
To begin watching an expression, typewatch('my_expression'). The commandwatchers will print the active watchers. To remove a watcher, typeunwatch('my_expression').
cont,c: Continue executionnext,n: Step nextstep,s: Step inout,o: Step outpause: Pause running code (like pause button in Developer Tools)setBreakpoint(),sb(): Set breakpoint on current linesetBreakpoint(line),sb(line): Set breakpoint on specific linesetBreakpoint('fn()'),sb(...): Set breakpoint on a first statement infunction's bodysetBreakpoint('script.js', 1),sb(...): Set breakpoint on first line ofscript.jssetBreakpoint('script.js', 1, 'num < 4'),sb(...): Set conditionalbreakpoint on first line ofscript.js that only breaks whennum < 4evaluates totrueclearBreakpoint('script.js', 1),cb(...): Clear breakpoint inscript.json line 1It is also possible to set a breakpoint in a file (module) thatis not loaded yet:
$node inspect main.js< Debugger listening on ws://127.0.0.1:9229/48a5b28a-550c-471b-b5e1-d13dd7165df9< For help, see: https://nodejs.org/en/docs/inspector<< Debugger attached.< okBreak on start in main.js:1>1 const mod = require('./mod.js'); 2 mod.hello(); 3 mod.hello();debug>setBreakpoint('mod.js', 22)Warning: script 'mod.js' was not loaded yet.debug>cbreak in mod.js:22 20 // USE OR OTHER DEALINGS IN THE SOFTWARE. 21>22 exports.hello =function() { 23 return 'hello from module'; 24 };debug>It is also possible to set a conditional breakpoint that only breaks when agiven expression evaluates totrue:
$node inspect main.js< Debugger listening on ws://127.0.0.1:9229/ce24daa8-3816-44d4-b8ab-8273c8a66d35< For help, see: https://nodejs.org/en/docs/inspector< Debugger attached.Break on start in main.js:7 5 } 6>7 addOne(10); 8 addOne(-1); 9debug>setBreakpoint('main.js', 4,'num < 0') 1 'use strict'; 2 3 function addOne(num) {>4return num + 1; 5 } 6 7 addOne(10); 8 addOne(-1); 9debug>contbreak in main.js:4 2 3 function addOne(num) {>4return num + 1; 5 } 6debug>exec('num')-1debug>backtrace,bt: Print backtrace of current execution framelist(5): List scripts source code with 5 line context (5 lines before andafter)watch(expr): Add expression to watch listunwatch(expr): Remove expression from watch listwatchers: List all watchers and their values (automatically listed on eachbreakpoint)repl: Open debugger's repl for evaluation in debugging script's contextexec expr,p expr: Execute an expression in debugging script's context andprint its valuerun: Run script (automatically runs on debugger's start)restart: Restart scriptkill: Kill scriptscripts: List all loaded scriptsversion: Display V8's versionV8 Inspector integration allows attaching Chrome DevTools to Node.jsinstances for debugging and profiling. It uses theChrome DevTools Protocol.
V8 Inspector can be enabled by passing the--inspect flag when starting aNode.js application. It is also possible to supply a custom port with that flag,e.g.--inspect=9222 will accept DevTools connections on port 9222.
To break on the first line of the application code, pass the--inspect-brkflag instead of--inspect.
$node --inspect index.jsDebugger listening on ws://127.0.0.1:9229/dc9010dd-f8b8-4ac5-a510-c1a114ec7d29For help, see: https://nodejs.org/en/docs/inspector(In the example above, the UUID dc9010dd-f8b8-4ac5-a510-c1a114ec7d29at the end of the URL is generated on the fly, it varies in differentdebugging sessions.)
If the Chrome browser is older than 66.0.3345.0,useinspector.html instead ofjs_app.html in the above URL.
Chrome DevTools doesn't support debuggingworker threads yet.ndb can be used to debug them.