Node Inspector

Overview

Node Inspector is a debugger interface for node.js using the Blink Developer Tools (former WebKit Web Inspector).

Features

The Blink DevTools debugger is a great javascript debugger interface; it works just as well for node. Node Inspector supports almost all of the debugging features of DevTools.

• Navigate in your source files
• Set breakpoints (and specify trigger conditions)
• Break on exceptions
• Step over, step in, step out, resume (continue)
• Continue to location
• Disable/enable all breakpoints
• Inspect scopes, variables, object properties
• Hover your mouse over an expression in your source to display its value in a tooltip
• Edit variables and object properties
• (etc.)

Cool stuff

• Node Inspector uses WebSockets, so no polling for breaks.
• Remote debugging
• Live edit of running code, optionally persisting changes back to the file-system.
• Set breakpoints in files that are not loaded into V8 yet - useful for debugging module loading/initialization.
• Javascript from top to bottom :)
• Embeddable in other applications - see Embedding HOWTO for more details.

Known Issues

This is beta-quality code, so use at your own risk.

• Be careful about viewing the contents of Buffer objects, each byte is displayed as an individual array element; for most Buffers this will take too long to render.
• While not stopped at a breakpoint the console doesn’t always behave as you might expect. See issue #146.
• Profiler is not implemented yet. Have a look at node-webkit-agent in the meantime.
• Break on uncaught exceptions does not work because of missing support in node.
• Debugging multiple processes (e.g. cluster) is cumbersome.

Getting Started

Requirements

• node.js
  • version 0.8 or later
• npm
• A Blink-based browser (i.e. Google Chrome)

Install

• With npm

    $ npm install -g node-inspector
  

Enable debug mode

To use node-inspector, enable debugging on the node you wish to debug. You can either start node with a debug flag like:

$ node --debug your/node/program.js

or, to pause your script on the first line:

$ node --debug-brk your/short/node/script.js

Or you can enable debugging on a node that is already running by sending it a signal:

1. Get the PID of the node process using your favorite method. pgrep or ps -ef are good

$ pgrep -l node 2345 node your/node/server.js

1. Send it the USR1 signal

$ kill -s USR1 2345

Great! Now you are ready to attach node-inspector.

Windows

Windows does not support UNIX signals. To enable debugging, you can use an undocumented API function process._debugProcess(pid):

1. Get the PID of the node process using your favorite method, e.g.

   > tasklist /FI "IMAGENAME eq node.exe"
   
   Image Name PID Session Name Session# Mem Usage
   ========================= ======== ================ =========== ============
   node.exe 3084 Console 1 11,964 K
   

2. Call the API:

   > node -e "process._debugProcess(3084)"
   

Great! Now you are ready to attach the inspector.

Debugging

1. start the inspector. I usually put it in the background

$ node-inspector &

1. open http://127.0.0.1:8080/debug?port=5858 in Chrome

2. you should now see the javascript source from node. If you don’t, click the scripts tab.

3. select a script and set some breakpoints (far left line numbers)

4. then watch the screencasts

For more information on getting started see the wiki

node-inspector works almost exactly like the web inspector in Chrome. Here’s a good overview of the UI

Inspector options

Node-inspector uses rc [github] module to collect options.

Places for configuration:

• command line arguments (parsed by optimist)
• enviroment variables prefixed with node-inspector_
• if you passed an option --config file then from that file
• a local .node-inspectorrc or the first found looking in ./ ../ ../../ ../../../ etc.
• $HOME/.node-inspectorrc
• $HOME/.node-inspector/config
• $HOME/.config/node-inspector
• $HOME/.config/node-inspector/config
• /etc/node-inspectorrc
• /etc/node-inspector/config
• options from config.json for backward compatibility
• defaults described in Node Inspector`s ./lib/config.js.

All configuration sources that where found will be flattened into one object, so that sources earlier in this list override later ones.

List of predefined options:

         Option Default Description
    --help | | Print information about options
    --web-port | 8080 | Port to host the inspector
    --web-host | 127.0.0.1 | Host to listen on
    --debug-port | 5858 | Port to connect to the debugging app
    --save-live-edit | false | Save live edit changes to disk (update the edited files)
    --hidden | [] | Array of files to hide from the UI
                      | | Breakpoints in these files will be ignored

FAQ / WTF

1. My script runs too fast to attach the debugger.

use --debug-brk to pause the script on the first line

1. I got the ui in a weird state.

when in doubt, refresh

1. Can I debug remotely?

Yes. node-inspector must be running on the same machine, but your browser can be anywhere. Just make sure port 8080 is accessible

1. How to specify list of files to hide?

Create a JSON-encoded array, don’t forget to escape the quote characters when using a command-line option.

$ node-inspector --hidden=’[“node_modules/framework”]’

Note that the array items are interpreted as regular expressions.

1. UI doesn’t load or doesn’t work and refresh didn’t help

Make sure that you have adblock disabled as well as any other content blocking scripts and plugins.

Contributing Code

Making Node Inspector the best debugger for node.js cannot be achieved without the help of the community. The following resources should help you to get started.

• Contributing
• Developer’s Guide
• Easy Picks

Thanks

Danny Coates for starting the project and maintaining it for several years.

StrongLoop for upgrading to the Blink front-end and maintaining the project onwards.

And of course all developers that contributed patches and features, as listed in the AUTHORS file.