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?
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
Debugging
Joyent's Guide
Debugger
Node Inspector
Visual Studio Code
Cloud9
Brackets
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
Caterpillar
Tracer
scribbles
Libraries that enhance stack trace information
Longjohn
Benchmarking
Apache Bench: ab -n 100000 -c 1 http://127.0.0.1:9778/
wrk
Other
Trace
Vantage
Bugger
Google Tracing Framework
Paul Irish's Guide
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These use to work but are no longer maintained or no longer applicable to modern node versions.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
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.
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.
Node.js version 0.3.4+ has built-in debugging support.
node debug script.js
Manual: http://nodejs.org/api/debugger.html
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.
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.
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
RisingStack - Debugging Node.js Applications
Excellent article by David Mark Clements of nearForm
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
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.
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.
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...
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.
An opensource cross-platform visual debugger.
Installation:
npm install iron-node -g;
Debug:
iron-node yourscript.js;
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()
If you are using the Atom IDE, you can install the node-debugger package.
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.
There is built-in command line debugger client within Node.js. Cloud 9 IDE have also pretty nice (visual) debugger.
I put together a short Node.js debugging primer on using the node-inspector for those who aren't sure where to get started.
Visual Studio Code will work for us in debugging.
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
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.
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.
Just for completeness:
The PyCharm 3.0 + Node.js Plugin offers an awesome development + run + debug experience.
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
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.
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.
IntelliJ works wonderfully for Node.js.
In addition, IntelliJ supports 'Code Assistance' well.
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:
NetBeans Wiki / NewAndNoteworthyNB81.
Node.js Express App in NetBeans IDE, Geertjan-Oracle.
Use this commands
DEBUG_LEVEL=all node file.js
DEBUG=* node file.js
node file.js --inspect
ndb is an improved debugging experience for Node.js, enabled by Chrome DevTools
https://github.com/GoogleChromeLabs/ndb
node-debug -p 8888 scriptFileName.js
Related
Yes, I use F12 in the browser all the time to test out Javascript snippets with the console. I'm tired of that (for the moment anyway).
I've read that in Visual Studio you can use the immediate window to run Javascript interactively.. I've haven't tried it that hard. I think when I did it told me it can't evaluate while in design mode... ugh, what a pain.
I do like to use Visual Studio Code (sublime text historically) sometimes to just mess around with syntax of snippets. Would also be nice if I could just run Javascript there too quickly. Is there a package I could download in VSCode to do so? Or something already built in?
As of (at least) my current version of VS Code (1.5.2), the "Debug Console", while debugging, lets you run arbitrary JavaScript code as you would in the VS Immediate Window. (Similar to as you would for the Chrome Dev Tools Console.)
There is no Immediate Window unlike Visual Studio in VSCode. But you can still execute Javascript in VSCode.
Install the Code Runner Extension - https://marketplace.visualstudio.com/items?itemName=formulahendry.code-runner
Open the JavaScript file in VSCode, then use shortcut Ctrl+Alt+N, the code will run and the output will be shown in the Output Window.
I've found this extension that makes a scrathpad for JS, that runs at the same time as you are typing: https://quokkajs.com/
Works on VS Code, Jet Brains, and Atom.
If you don't want to start a debugging session or installing an extension, a simple way to have a JavaScript console is to start Node in a Terminal.
View -> Terminal
Start node (without any argument -you'll need node in your PATH)
Now you have a repl with auto-complete and value preview.
It doesn't have the features of the Chrome Console, but I find it good enough for evaluating JS code while I'm working.
Run the command node in the terminal below the editor, this will create a node environment where arbitrary JavaScript can be entered. You must first have node (and apparently npm) installed from nodejs.
This might do it: https://code.visualstudio.com/Docs/runtimes/nodejs
Node.js is a platform for building fast and scalable server applications using JavaScript. Node.js is the runtime and NPM is the Package Manager for Node.js modules.
To get started, install Node.js for your platform. The Node Package Manager is included in the Node distribution.
I often develop in Python and sometimes find it useful to type python at the terminal prompt and drop into a Python shell where I can import various modules and test some behavior. Node.js has similar functionality if I type node at the command line.
I'd like to do the same now that I'm developing with Meteor. How can I get to a shell prompt where all the packages I have added with meteor add are loaded and ready for me to play with?
Just install node-inspector and then you can easily use the node-debug command to run node-debug mrt. That should open a debugger console.
You can then just drop a debugger; keyword onto a line anywhere in your code to drop into a REPL like setting.
As of recently, meteor shell will give you a REPL into the server process.
Of course, you know this #JoshOwens, I think I heard about this on your podcast :)
Node.js and python are both interpreters.
Meteor is a application framework build upon node.js. So testing out code in the way you mentioned is impossible.
You can however use the chrome debugging tools to run client side code within your meteor application.
Executing server side code to see what it does is a bit harder but also not impossible. Best way would probaply to setup nodejs remote debugging and using the debugger. See: Meteor debugging setup
I want to run some javascript code (unit and interaction tests) right in visual studio and be able to see console output. Is it possible to do that with VS???
Node.js Tools for Visual Studio has a REPL for node.js that can be used for such things.
I love the Interactive Window for Visual Studio (and 2017) but lately I have been starting to use Visual Studio Code. I really like it but the Interactive Window (REPL) is missing.
I need that. So I tried several extensions but none of them was as good as Node.js Tools for VS. The solution was to make one my self, you may need NodeJs 8+ to use Node.js REPL for Visual Studio Code.
Preview of Node.js REPL for VS Code
I believe it is possible, at least to a degree. I haven't done exactly what you're saying, but I do have node running in iis with iisnode. I also know that there is a version of iisnode that runs under iis express. I would look into that.
My guess is you would be able to launch a project using the iisnode module, and you could set the default document to the .js file you want to run, but you may only be able to get console output through the browser.
iisnode does give you the ability to debug and see the console output through your browser. For example, if you run the iisnode module for a file test.js at localhost:1234/test.js, you can get a the browser developer tools by going to localhost:1234/test.js/debug. That would give you console output, but I'm not totally certain you would be able to get it directly in VS.
I'm trying to build the Chrome V8 javascript engine so I can embed it into my c++ project. I'm following the tutorial here. I downloaded everything that was needed and managed to get the project solution created but when I compile it only 5 of the 12 solutions get compiled correctly. Can someone shed some light on my problem? There doesn't seem to be much info on the web about it.
Some tricks I learned are this:
use the correct gyp command that will generate correct sln files. maybe target architecture argument was wrong or some other parameter you supply to gyp.
I do not know how to properly "clean" the source tree, so if I wanted new options to gyp I just delete the whole source tree and unpack from original archive. (or use svn).
Make sure you use python and cygwin supplied with v8 sources.
I used pc emulator (qemu) to install Windows XP + Visual studio and v8 sources+tools.
I tried various versions of Visual Studio only VS Express 2010 worked.
On linux everything is simpler. And you do not even need to build it, just use "aptitude install v8-dev"
I'm curious if anyone has a solution for running meteor in a debugger. I have some experience with running regular node in a debugger, have used JetBrains Webstorm for this, however it doesn't seem to support meteor (as far as I can tell). If anyone has a solution, would appreciate any information. It seems, eventually this will need to be possible for meteor to become a longterm viable platform.
It looks like the meteor startup script does not support a debugging option at this point, but you can fix this yourself:
Open the meteor startup script in a text editor (use which meteor to find it)
Change the last line (add $NODE_DEBUG parameter):
exec "$DEV_BUNDLE/bin/node" $NODE_DEBUG "$METEOR" "$#"
Now you can launch meteor in debug mode like this:
NODE_DEBUG=--debug meteor