How do I debug Node.js applications?

Question

How do I debug a Node.js server application?

Right now I’m mostly using alert debugging with print statements like this:

sys.puts(sys.inspect(someVariable));

There must be a better way to debug. I know that Google Chrome has a command-line debugger. Is this debugger available for Node.js as well?

If you want to debug with the traditional IDE appoach, use vscode use vscode youtube.com/watch?v=egBJ0cd0GLM — jw56578
I have found this article very interesting, and it works for me just fine: Debugging Node.js with Chrome DevTools. Hope it helps 🙂 — Timbergus
Keep in mind that you need to run nod with --inspect-brk INSTEAD OF --inspect if you want to debug the actual server code at load time. See stackoverflow.com/questions/59596138 — Jorge Orpinel Pérez

daralthus · Accepted Answer · 2010-10-15T17:17:02

node-inspector could save the day! Use it from any browser supporting WebSocket. Breakpoints, profiler, livecoding, etc… It is really awesome.

Install it with:

npm install -g node-inspector

Then run:

node-debug app.js

daralthus

17

Wish node-inspector was active. The profiling component needs to get some love.
– Jonathan Dumaine
Unfortunately for me, node-inspector doesn’t work with the latest versions of Node.js and it hasn’t supported logging to the browser console since v0.1. node-codein was just buggy. So, I wrote my own module to help with debugging by allowing you to dump objects and such out to your web browser console. I thought it may be of use to someone else: node-monkey. Plus it works in both Firefox AND Chrome.
– Justin Warkentin
Since this was such an apparently amazing and popular tool, surely the fact that the original author has admitted they no longer have the resources to maintain it wouldn’t be a problem as the open source community could pick it up?
– PeterT
Now inspector is now actively maintained by StrongLoop and is working again with the latest version (0.3) yay! Announcement here: blog.strongloop.com/…
– balupton
“Since version 6.3, Node.js provides a buit-in DevTools-based debugger which mostly deprecates Node Inspector, see e.g. this blog post to get started. The built-in debugger is developed directly by the V8/Chromium team and provides certain advanced features (e.g. long/async stack traces) that are too difficult to implement in Node Inspector.” – says the node inspector repo
– ThisClark

codemeasandwich · Accepted Answer · 2013-05-12T21:37:33

Debugging

Profiling

node --prof ./app.js
node --prof-process ./the-generated-log-file

Heapdumps

node-heapdump with Chrome Developer Tools

Flamegraphs

0x
jam3/devtool then Chrome Developer Tools Flame Charts
Dtrace and StackVis — Only supported on SmartOS
clinicjs

Tracing

Interactive Stack Traces with TraceGL

Logging

Libraries that output debugging information

Libraries that enhance stack trace information

Longjohn

Benchmarking

Apache Bench: ab -n 100000 -c 1 http://127.0.0.1:9778/
wrk

Other

Legacy

These use to work but are no longer maintained or no longer applicable to modern node versions.

https://github.com/bnoordhuis/node-profiler – replaced by built-in debugging
https://github.com/c4milo/node-webkit-agent – replaced by node inspector
https://nodetime.com/ – defunct

About Nodetime: for those who don’t want to send their data to nodetime servers there’s a local “alternative” (it’s still based on nodetime), the look module, as pointed out in stackoverflow.com/questions/12864221/nodejs-memory-profiling — reallynice
I don’t find the cpu reports from nodetime very helpful: 1. I just get a tree of methods, with no ‘self’ time. 2. Seems like the tree branches are trimmed below a certain number of precentage. Those 2 makes it very difficult to undestand where the cpu spends most of its time. — shacharz
npm install -g profiler complains about missing python on windows 7. I tried to set python=C:Python34, but this gives a crash. — Stepan Yakovenko
The only profiler working out of the box is nodetime. But its cpu profiling stacktrace is unusable (it doesn’t give enough details). Nodejs tools 4 msvc 2012 also have profiler, but it also has reported critical unfixed bug… — Stepan Yakovenko
The only profiler that worked for me was nprof + v8.log from node --prof. — Dan Abramov

d4nyll · Accepted Answer · 2010-03-29T08:57:06

The V8 debugger released as part of the Google Chrome Developer Tools can be used to debug Node.js scripts. A detailed explanation of how this works can be found in the Node.js GitHub wiki.

d4nyll

7

I’m interested, after the presentation at Google IO that Paul Irish and Pavel did is it now possible to debug node.js straight to Chrome Developer Tools without the need for eclipse?
– balupton
+1 Worked very well for me. Using a fresh Eclipse 3.x, x64 version on Mac OS X. The installation instructions are well written as well. Thank you.
– amateur barista
Also comes within Nodeclipse nodeclipse.org (with some Node.js related bugs fixed)
– Paul Verest
My entry into this arena is trepanjs (npmjs.com/package/trepanjs). It has all of the goodness of the node debugger, but conforms better to gdb. It also has more features and commands like syntax highlighting, more extensive online help, and smarter evaluation. See github.com/rocky/trepanjs/wiki/Cool-things for some of its cool features.
– rocky
The feature is currently available in the nightly versions. Check out here for instructions: https://medium.com/@paul_irish/debugging-node-js-nightlies-with-chrome-devtools-7c4a1b95ae27#.fitvuaumt
– zeronone

Alister · Accepted Answer · 2016-09-14T14:51:34

Node has its own built in GUI debugger as of version 6.3 (using Chrome’s DevTools)

Simply pass the inspector flag and you’ll be provided with a URL to the inspector:

node --inspect server.js

You can also break on the first line by passing --inspect-brk instead.

Alister

8

Not to discount the steps above, but just to share… I attempted to create a wrapper that is slightly more robust, as well as easier to install. See: github.com/jaridmargolin/inspect-process
– Jarid R. Margolin
@JaridR.Margolin Nice. I updated the answer to use that instead. A lot easier to setup and works better 🙂
– gregers
This answer is currently at the bottom and it’s the only one that has actually worked for me. This is flipping awesome!
– LOAS
In case it helps anyone, I threw up a video explaining this process at youtu.be/rtZKUnks6jI.
– RoccoB
Where did you got the dark theme for the chrome developer tools?
– Pieter Meiresone

Salman von Abbas · Accepted Answer · 2011-01-16T01:20:53

Node.js version 0.3.4+ has built-in debugging support.

node debug script.js

Manual: http://nodejs.org/api/debugger.html

Salman von Abbas

JulianW

6

Do you have any links to documentation of how to use it?
–
I don’t have any docs. just updated to v0.3.5. put a line “debugger;” in your code which will act as break point. It works like ndb / gdb. after you do “node debug script.js” type help. u will see the command it support. p = print, l = list… so you don’t need to type the full world
– JulianW
Note, under windows it’s “node.exe –debug myscript.js” but it still don’t work.
– Marc
You probably have to change --debug to debug without the dashes. That’s how I finally got it to work. It’s confusing that --debug and debug do two different things.
– benekastah
How do you get the program to actually run? “r -> app is already running...“, when i try to continue and i run into a statement that is trying to get input it drops me back at the debug prompt instead of letting me enter the input that is required.
– Michael

Shreyas · Accepted Answer · 2016-02-19T10:21:40

Visual Studio Code will be my choice for debugging. No overhead of installing any tools or npm install stuff.
Just set the starting point of your app in package.json and VSCode will automatically create a configuration file inside your solution. It’s build on Electron, on which editors like Atom are built.

VS Code gives similar debugging experience as you might have
had in other IDEs like VS, Eclipse, etc.

It’s cool but it has lag. That’s why I do prefer Sublime ever. — calbertts
but sublime doesn’t have a debugger,and i think VS code is pretty fast too — Syed Faizan
I’ve a sublime license since 5 years ago. Since a few months ago I don’t even install Sublime Text, just vscode. Out of the box has a lot of tools which I miss in Sublime (like the integrated terminal..). — elboletaire
always asking me for a config folder, it doesn’t work out of the box — carkod
@carkod enable vs code auto attach preference and use the vs code terminal to start your script, ex node –inspect file-name.js — Vipul Dessai

Peter Mortensen · Accepted Answer · 2012-05-03T14:42:13

I personally use JetBrains WebStorm as it’s the only JavaScript IDE that I’ve found which is great for both frontend and backend JavaScript.

It works on multiple OS’s and has Node.js debugging built-in (as well as a ton of other stuff](http://www.jetbrains.com/webstorm/features/index.html).

My only ‘issues’/wishlist items ~~are~~ were:

~~It seems to be more resource hungry on Mac than Windows~~ It no longer seems an issue in version 6.
~~It would be nice if it had Snippet support (like those of Sublime Text 2 – i.e. type ‘fun’ and tap ‘tab’ to put in a function.~~ See @WickyNilliams comment below – With Live Templates you also have snippet support.

webstorm does have snippet support BTW 😉 though they’re known as “Live Templates” instead of snippets. — WickyNilliams
If you just want to debug a node.js app and already have an Intellij IDEA license you can just install the node.js plugin without having to buy the WebStorm license. Setting up a run/debug config is very easy once the plugin is installed. — Josh Liptzin

Philip O’Brien · Accepted Answer · 2015-09-15T15:33:22

A lot of great answers here, but I’d like to add my view (based on how my approach evolved)

Debug Logs

Let’s face it, we all love a good console.log('Uh oh, if you reached here, you better run.') and sometimes that works great, so if you’re reticent to move too far away from it at least add some bling to your logs with Visionmedia’s debug.

Interactive Debugging

As handy as console logging can be, to debug professionally you need to roll up your sleeves and get stuck in. Set breakpoints, step through your code, inspect scopes and variables to see what’s causing that weird behaviour. As others have mentioned, node-inspector really is the bees-knees. It does everything you can do with the built-in debugger, but using that familiar Chrome DevTools interface.
If, like me, you use Webstorm, then here is a handy guide to debugging from there.

Stack Traces

By default, we can’t trace a series of operations across different cycles of the event loop (ticks). To get around this have a look at longjohn (but not in production!).

Memory Leaks

With Node.js we can have a server process expected to stay up for considerable time. What do you do if you think it has sprung some nasty leaks? Use heapdump and Chrome DevTools to compare some snapshots and see what’s changing.

For some useful articles, check out

If you feel like watching a video(s) then

Netflix JS Talks – Debugging Node.js in Production
Interesting video from the tracing working group on tracing and debugging node.js
Really informative 15-minute video on node-inspector

Whatever path you choose, just be sure you understand how you are debugging

It is a painful thing
To look at your own trouble and know
That you yourself and no one else has made it
Sophocles, Ajax

Sindre Sorhus · Accepted Answer · 2013-05-14T22:21:22

Theseus is a project by Adobe research which lets you debug your Node.js code in their Open Source editor Brackets. It has some interesting features like real-time code coverage, retroactive inspection, asynchronous call tree.

screenshot

Sindre Sorhus

2

this is pretty cool, still don’t know what’s Backtrace for tho
– misaxi
I’m currently loving Theseus, but I still have some problems where I need to set a breakpoint and trace through. I’m currently having to kill my app, start node with –debug, trace trhough and then start the app with node-theseus. Is it possible to use Theseus with breakpoints? I’ve tried searching around the GitHub page, StackOverflow and forums, but with no luck so far. Am I missing something?
– Eugene

Peter Mortensen · Accepted Answer · 2014-05-02T12:30:11

Node.js Tools for Visual Studio 2012 or 2013 includes a debugger. The overview here states “Node.js Tools for Visual Studio includes complete support for debugging node apps.”. Being new to Node.js, but having a background in .NET, I’ve found this add in to be a great way to debug Node.js applications.

Peter Mortensen · Accepted Answer · 2015-09-09T00:08:22

Visual Studio Code has really nice Node.js debugging support. It is free, open source and cross-platform and runs on Linux, OS X and Windows.

You can even debug grunt and gulp tasks, should you need to…

Peter Mortensen

hans

2

Starting from Visual Studio Code 8.0 the debugging support for OSX and Linux got really good.
– bgse
After spending a whole evening getting node-inspector and strongloop to function under windows (Visual Studio Community, downgrade to npm 2, installing python, env variables, use cmd not babun / cygwin etc. etc.) and then playing with this for an hour, I have to say this is the best option at least in windows and possibly in general (if you don’t have webstorn)
– dashambles

Community · Accepted Answer · 2015-07-19T15:10:04

I wrote a different approach to debug Node.js code which is stable and is extremely simple. It is available at https://github.com/s-a/iron-node.

Enter image description here

An opensource cross-platform visual debugger.

Installation:

npm install iron-node -g;

Debug:

iron-node yourscript.js;

Peter Mortensen · Accepted Answer · 2015-03-30T04:04:35

If you are using the Atom IDE, you can install the node-debugger package.

babidi · Accepted Answer · 2018-06-04T12:21:56

Using Chrome Version 67.0.3396.62(+)

Run node app

node –inspect-brk=0.0.0.0:9229 server.js(server js filename)

Browse your app in chrome e.g. “localhost:port”
Open DevTools.
Click the the node icon beside the responsive device icon.

There will be another DevTools window that will pop out specifically for debugging node app.

keen · Accepted Answer · 2014-12-09T15:22:41

I created a neat little tool called pry.js that can help you out.

Put a simple statement somewhere in your code, run your script normally and node will halt the current thread giving you access to all your variables and functions. View/edit/delete them at will!

var pry = require('pryjs')

class FizzBuzz

  run: ->
    for i in [1..100]
      output=""
      eval(pry.it) // magic
      output += "Fizz" if i % 3 is 0
      output += "Buzz" if i % 5 is 0
      console.log output || i

  bar: ->
    10

fizz = new FizzBuzz()
fizz.run()

keen · Accepted Answer · 2011-03-11T19:29:53

There is built-in command line debugger client within Node.js. Cloud 9 IDE have also pretty nice (visual) debugger.

Cloud 9 is way to go for me, especially gives freedom of code anywhere option without carrying my laptop. — Teoman shipahi

Josh Habdas · Accepted Answer · 2013-11-21T18:31:17

I put together a short Node.js debugging primer on using the node-inspector for those who aren’t sure where to get started.

Surendra Parchuru · Accepted Answer · 2017-10-15T10:02:20

Visual Studio Code will work for us in debugging.

OneMoreQuestion · Accepted Answer · 2016-07-25T19:13:43

Use Webstorm! It’s perfect for debugging Node.js applications. It has a built-in debugger. Check out the docs here: https://www.jetbrains.com/help/webstorm/2016.1/running-and-debugging-node-js.html

Peter Mortensen · Accepted Answer · 2012-03-08T01:46:52

If you need a powerful logging library for Node.js, Tracer https://github.com/baryon/tracer is a better choice.

It outputs log messages with a timestamp, file name, method name, line number, path or call stack, support color console, and support database, file, stream transport easily. I am the author.

Peter Mortensen · Accepted Answer · 2013-04-29T01:20:36

Assuming you have node-inspector installed on your computer (if not, just type ‘npm install -g node-inspector’) you just have to run:

node-inspector & node --debug-brk scriptFileName.js

And paste the URI from the command line into a WebKit (Chrome / Safari) browser.

node-inspector was already mentioned; maybe delete this answer? — Dan Dascalescu

Peter Mortensen · Accepted Answer · 2014-02-05T01:27:05

Just for completeness:

The PyCharm 3.0 + Node.js Plugin offers an awesome development + run + debug experience.

Rahul Kumar · Accepted Answer · 2018-02-09T19:05:32

Start your node process with –inspect flag.

node --inspect index.js

and then Open chrome://inspect in chrome. Click the “Open dedicated DevTools for Node” link or install this chrome extension for easily opening chrome DevTools.

For more info refer to this link

Glorfindel · Accepted Answer · 2014-01-02T05:24:39

There is the new open-source Nodeclipse project (as a Eclipse plugin or Enide Studio):

Nodeclipse became #1 in Eclipse Top 10 NEW Plugins for 2013. It uses a modified V8 debugger (from Google Chrome Developer Tools for Java).

Nodeclipse is free open-source software released at the start of every month.

卢声远 Shengyuan Lu · Accepted Answer · 2015-08-05T03:34:42

IntelliJ works wonderfully for Node.js.

In addition, IntelliJ supports ‘Code Assistance’ well.

cmd · Accepted Answer · 2017-01-21T06:13:29

There are many possibilities…

node includes a debugging utility
node-inspector
Code editors / IDEs (see debug instructions for one of the following)
- Atom,
- VSCode
- Webstorm
- and more

Debug support is often implemented using the v8 Debugging Protocol or the newer Chrome Debugging Protocol.

Peter Mortensen · Accepted Answer · 2015-11-24T08:26:37

The NetBeans IDE has had Node.js support since version 8.1:

<…>
New Feature Highlights
Node.js Application Development

New Node.js project wizard

New Node.js Express wizard

Enhanced JavaScript Editor

New support for running Node.js applications

New support for debugging Node.js applications.
<…>

Additional references:

Zahirul Haque · Accepted Answer · 2018-03-24T01:51:59

Use this commands

DEBUG_LEVEL=all node file.js
DEBUG=* node file.js
node file.js --inspect

Mukesh · Accepted Answer · 2018-12-11T19:52:44

ndb is an improved debugging experience for Node.js, enabled by Chrome DevTools

https://github.com/GoogleChromeLabs/ndb

matt burns · Accepted Answer · 2014-05-07T15:53:27

node-debug -p 8888 scriptFileName.js

42 Answers
42

Debugging

Profiling

Heapdumps

Flamegraphs

Tracing

Logging

Benchmarking

Other

Legacy

Node has its own built in GUI debugger as of version 6.3 (using Chrome’s DevTools)

Debug Logs

Interactive Debugging

Stack Traces

Memory Leaks

New Feature Highlights

Node.js Application Development

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How do I debug Node.js applications?

42 Answers 42

Debugging

Profiling

Heapdumps

Flamegraphs

Tracing

Logging

Benchmarking

Other

Legacy

Node has its own built in GUI debugger as of version 6.3 (using Chrome’s DevTools)

Debug Logs

Interactive Debugging

Stack Traces

Memory Leaks

New Feature Highlights

Node.js Application Development

42 Answers
42