How to debug node js app with breakpoints and everything?

Question

I've installed node-inspector just to find out that it doesn't support breakpoints :| What's the point in it at all, bearing in mind that on big part node code is asynchronous and you simply cannot follow it step by step?..

I'm definitely missing a point here...

Anyway to debug node code with breakpoints and everything?

• beny23: Possible duplicate: stackoverflow.com/questions/1911015/…
• jayarjo: I came here from there - breakpoints do not work in node-inspector and there is no answer to my question. Is there?
• JP Richardson: It does support breakpoints. I just doesn't 'remember' them when you referesh the inspector page.
• Ciro Santilli OurBigBook.com: Possible duplicate of How do I debug Node.js applications?
• jayarjo: Debugging node.js applications has become much better these days. So this question and answers are probably not even actual anymore.

Answer 1

yupp, I've successfully used node-inspector. If you want permanent breakpoints, simply insert debugger; in your code. See http://nodejs.org/api/debugger.html.

Making node wait until a debugger is attached, using node --inspect-brk script.js (previously node --debug-brk script.js), can also be very helpful.

• jayarjo: with debugger; it crashes: node(31848,0x7fff70e12cc0) malloc: *** error for object 0x10010f690: pointer being freed was not allocated *** set a breakpoint in malloc_error_break to debug Abort trap
• rdrey: I've never seen that error, sorry. Is your app's process crashing, or is it node-inspector? Which versions are you running? Are you using any native node modules that could be crashing?
• MegaMatt: For later versions of Node.js, --debug-brk is deprecated. Use --inspect-brk instead.

Answer 2

(For Node 8 and later)

Node.js has a built-in debugger. Normally you can turn on the debugger in two ways:

1. Start your Node.js app or script with the --inspect or --inspect-brk switch. For example:

   $ node.js --inspect index.js

(Note: --inspect-brk breaks before user code starts)

2. If for some reason you cannot start your Node.js app or script with the --inspect switch, you can still instruct the Node.js process to start listening for debugging messages by signalling it with SIGUSR1 (on Linux and OS X). For Node 8 and later it will activate the Inspector API, same as the --inspect switch

   $ kill -sigusr1 23485

(Note: you need to replace 23485 with your own Node.js process ID)

With the debugger turned on, you can open the Google Chrome browser, and type in the address bar chrome://inspect

Then you should see an entry listed under "Remote Target". Go ahead and click "inspect".

Now you can set breakpoints and start debugging your code.

Reference:

1. https://nodejs.org/en/docs/guides/debugging-getting-started/
2. Related issue on stackoverflow: Chrome Devtools Dedicated Node.js Inspector not stopping at breakpoints

• Ciro Santilli OurBigBook.com: To do everything in the terminal, you need node inspect instead as explained at: stackoverflow.com/a/55429798/895245 as of v10.15.1.
• Benny Neugebauer: I've made a video which shows the inspect setup with Node.js (and TypeScript if needed): youtube.com/watch?v=bV-DHjmwuZ0

Answer 3

To debug a Node.js application, one can use the debugging built-in method:

(1) Insert debugger; statement where you want to insert a break point
(2) Run the file with command $ node inspect <file name>
(3) Use a key for example, c to continue to next break point

You can even debug values associated to variables at that break point by typing repl. For more information, Please check the official guide.

• Ciro Santilli OurBigBook.com: Tested on v10.15.1.
• Jean Paul: If you don't want to modify your code, you can use the function setBreakpoint or sb to set up a breakpoint, eg setBreakpoint('script.js', 1) (nodejs.org/api/debugger.html)

Answer 4

Have you tried using nodemon library? it can be found here.

For development purposes you could start the app running nodemon. I have this script:

"dev": "nodemon --inspect src/index.js"

It will break any time a debugger statement is reached in the code. To open the console where you can see the server code, open the console in chrome and click on the nodejs icon:enter image description here

It also helps you refreshing the server every time you save any file on the server.

Let me know if it works!

Answer 5

Just to elaborate a bit here:

Set a debugger wherever you want the breakpoints to be and then run your code with node debug script.js/index.js

When the debugger stops at you breakpoint, you will need to repl to inspect the variables.

• Michael: i want a breakpoint wherever an exception happens (let's say I don't know ahead of time where that will be). how do i do that?
• Tarandeep Singh: you can instead of using REPL command add runtime watchers, just type for ex. watch('count') watchers api will print the value when debugger stops in that function.