How to debug node / express?

Question

When I start my app using 'npm start' at the command line I can browse it at :3000

.. but not when I start it using 'node app.js'

when I try 'node --debug app.js' I get a console window with the message

"Debugger listening on port 5858"

With Visual Studio and the node toolkit I get the same. With Eclipse and Enide I get the same.

I've tried using Nodes built in command line debugger, but after the debug> prompt appears issuing the continue or next step commands does nothing, and I can't browse the app at :3000

I've installed node-inspector, and after 'node --debug app.js' I can see app.js in the node-inspector chrome tab :8080, but can't browse my app at :3000 and can't get breakpoints to work.

I guess that to get debugging working I need 'node app.js' to run, and not be using 'npm start'..

What important node configuration detail have I missed?

Why is my app not browsable when using 'node app.js' ?

Any advice is appreciated..

Ben · Accepted Answer · 2015-07-19 23:28:01Z

2

Your actually starting the app in two differnet ways using different code - one which includes the debugger and one that does not.

If your running a default Express 4 setup, if you check the package.json file you will see this section:

"scripts": {
    "start": "node ./bin/www"
  }

That is the file that is executed when you run npm start, so running node app.js is actually a different script.

If you take a look at bin/www you will see the debugger is invoked:

var debug = require('debug')('myapp');

To run use:

DEBUG=myapp ./bin/www

If you are starting using NPM, you can add it to the package.json or use exactly the same command from the cmd line:

"scripts": {
    "start": "DEBUG=myapp node ./bin/www"
  }

edited Jul 19, 2015 at 23:28

answered Jul 19, 2015 at 22:19

Ben

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4 Comments

Kickaha Over a year ago

Okay I see... 'npm start' is invoking the start script as defined in 'package.json', great that explains a lot... and I can tell visual studio/enide to use 'npm start' instead of 'node app.js' .... or use the command line... but where do I put 'DEBUG=myapp ./bin/www' so that node-inspector will attach? in the .bin/www script ?

Ben Over a year ago

@Kickaha I have not used node-inspector but it looks like you may be confusing the node-debug lib with the debug lib. Just had a real quick look at node-inspector and it looks like you just install globally and then kick it off using node-debug so node-debug ./bin/www should do it.

Kickaha Over a year ago

Okay I found that for Visual Studio I needed to hack the 'myApp.njsproj' project file to add bin/www as the startup file.. For Eclipse it is set in Run > Run Configurations > Node Configuration.. (I couldn't set breakpoints using Eclipse, but could use it in conjunction with node-inspector.. ) understanding that bin/www was a file and not a directory was key so cheers.. One other editor very good at express debugging I found was 'MS Code'. It's still in beta but is a much better tool for the job. I'll go back to the built in debugger if I need to debug in a terminal. Thanks again Ben.

Ben Over a year ago

Check out WebStorm (part of the intelliJ family). Its not free but by far the best IDE I have found for node. Great debug tools, integrated testing etc.

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