Debugger | Node.js v18.9.0 Documentation

Debuggerhttps://nodejs.org/api/debugger.html#debugger Stability: 2 - Stable Node.js includes a command-line debugging utility. The Node.js debugger client is not a full-featured debugger, but simple stepping and inspection are possible. To use it, start Node.js with the inspect argument followed by the path to the script to debug. $ node inspect myscript.js 2 global.x = 5; 3 setTimeout(() => { 4 debugger; debug> The debugger automatically breaks on the first executable line. To instead run until the first breakpoint (specified by a debugger statement), set the NODE_INSPECT_RESUME_ON_START environment variable to 1. $ cat myscript.js // myscript.js global.x = 5; setTimeout(() => { debugger; console.log('world'); }, 1000); console.log('hello'); $ NODE_INSPECT_RESUME_ON_START=1 node inspect myscript.js { > 4 debugger; 5 console.log('world'); 6 }, 1000); debug> next break in myscript.js:5 3 setTimeout(() => { 4 debugger; > 5 console.log('world'); 6 }, 1000); 7 console.log('hello'); debug> repl Press Ctrl+C to leave debug repl > x 5 > 2 + 2 4 debug> next 6 }, 1000); 7 console.log('hello'); 8 debug> .exit $ The repl command allows code to be evaluated remotely. The next command steps to the next line. Type help to see what other commands are available. Pressing enter without typing a command will repeat the previous debugger command. Watchershttps://nodejs.org/api/debugger.html#watchers It is possible to watch expression and variable values while debugging. On every breakpoint, each expression from the watchers list will be evaluated in the current context and displayed immediately before the breakpoint’s source code listing. To begin watching an expression, type watch('my_expression'). The command watchers will print the active watchers. To remove a watcher, type unwatch('my_expression'). Command referencehttps://nodejs.org/api/debugger.html#command-reference Steppinghttps://nodejs.org/api/debugger.html#stepping cont, c: Continue execution next, n: Step next step, s: Step in out, o: Step out pause: Pause running code (like pause button in Developer Tools) Breakpointshttps://nodejs.org/api/debugger.html#breakpoints setBreakpoint(), sb(): Set breakpoint on current line setBreakpoint(line), sb(line): Set breakpoint on specific line setBreakpoint('fn()'), sb(...): Set breakpoint on a first statement in function’s body setBreakpoint('script.js', 1), sb(...): Set breakpoint on first line of script.js setBreakpoint('script.js', 1, 'num < 4'), sb(...): Set conditional breakpoint on first line of script.js that only breaks when num 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> c break 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 a given expression evaluates to true: $ node inspect main.js 7 addOne(10); 8 addOne(-1); 9 debug> setBreakpoint('main.js', 4, 'num 4 return num + 1; 5 } 6 7 addOne(10); 8 addOne(-1); 9 debug> cont break in main.js:4 2 3 function addOne(num) { > 4 return num + 1; 5 } 6 debug> exec('num') -1 debug> Informationhttps://nodejs.org/api/debugger.html#information backtrace, bt: Print backtrace of current execution frame list(5): List scripts source code with 5 line context (5 lines before and after) watch(expr): Add expression to watch list unwatch(expr): Remove expression from watch list watchers: List all watchers and their values (automatically listed on each breakpoint) repl: Open debugger’s repl for evaluation in debugging script’s context exec expr, p expr: Execute an expression in debugging script’s context and print its value Execution controlhttps://nodejs.org/api/debugger.html#execution-control run: Run script (automatically runs on debugger’s start) restart: Restart script kill: Kill script Varioushttps://nodejs.org/api/debugger.html#various scripts: List all loaded scripts version: Display V8’s version Advanced usagehttps://nodejs.org/api/debugger.html#advanced-usage V8 inspector integration for Node.jshttps://nodejs.org/api/debugger.html#v8-inspector-integration-for-nodejs V8 Inspector integration allows attaching Chrome DevTools to Node.js instances for debugging and profiling. It uses the Chrome DevTools Protocol. V8 Inspector can be enabled by passing the --inspect flag when starting a Node.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-brk flag instead of --inspect. $ node --inspect index.js Debugger listening on ws://127.0.0.1:9229/dc9010dd-f8b8-4ac5-a510-c1a114ec7d29 For help, see: https://nodejs.org/en/docs/inspector (In the example above, the UUID dc9010dd-f8b8-4ac5-a510-c1a114ec7d29 at the end of the URL is generated on the fly, it varies in different debugging sessions.) If the Chrome browser is older than 66.0.3345.0, use inspector.html instead of js_app.html in the above URL. Chrome DevTools doesn’t support debugging worker threads yet. ndb can be used to debug them.