Runs Node.js programs inside Chrome DevTools (using Electron).
# runs a Node.js app in DevToolsdevtool src/app.js
This allows you to profile, debug and develop typical Node.js programs with some of the features of Chrome DevTools. See my blog post Debugging Node.js With Chrome DevTools for more details.
The recording below shows setting breakpoints within an HTTP server.
Note: This tool is still in early stages. So far it has only been tested on a couple of OSX machines. :)
Install globally with
npm install devtool -g
Run the command to open a new DevTools window.
Usage:devtool [entry] [opts]Options:--watch, -w enable file watching (for development)--quit, -q quit application on fatal errors--console, -c redirect console logs to terminal--index, -i specify a different index.html file--poll, -p enable polling when --watch is given--show, -s show the browser window (default false)--headless, -h do not open the DevTools window--timeout, -t if specified, will close after X seconds--break insert a breakpoint in entry point--config a path to .devtoolrc config file--verbose verbose Chromium logging--version, -v log versions of underlying tools--require, -r require path(s) before running entry--browser-field, --bf resolve using "browser" field--no-source-maps,--no-sm disable source map generation--no-node-timers,--no-nt use browser timers--no-browser-globals,--no-bg removes window,document,navigator from required files
# watch/dev a JS file, with a custom index.htmldevtool src/index.js --index index.html --watch# redirect console and pipe results to a filedevtool main.js -q -c > foo.txt# open a REPL windowdevtool# pipe content into process.stdindevtool writer.js < README.md# pass clean arg list to app.jsdevtool app.js --watch -- entry# register with babel before requiring our appdevtool -r babel-register app.js
You can specify
--watch multiple times to watch different files/globs. If a custom
--index is passed, it will also be watched for changes.
-- is given, anything after it will be used as the arguments for the app's
process.argv. This way you can avoid polluting your program arguments with those specific to
--bf makes the
require() statements respect the package.json
--no-bg flag makes required modules behave a little more like Node, in that
document and some other browser globals will be undefined in required files. Note: the console and REPL may still show some of these globals.
You can also specify advanced Electron/Node options in a
rc configuration file, such as DevTools themes and V8 flags. See rc configuration for more details.
See my blog post Debugging Node.js With Chrome DevTools for more details.
Debugging / Profiling
// build.jsvar browserify = ;// Start DevTools profiling...console;// Bundle some browser application;
Now we can run
devtool on our file:
Some screenshots of the profiling and debugging experience:
Note: Performance may vary between Node and Electron, so always take the results with a grain of salt!
You can also set an initial breakpoint with the
--break flag. This will insert a
debugger statement (hidden behind source maps) at the start of your entry file. This way, you can add breakpoints without having to reload the program or manually add them to your source code.
# run app but break on startdevtool src/index.js --break
We can also use the DevTools Console as a basic Node REPL with some nice additional features. The require statements will be relative to your current working directory. You can run the command without any entry file, like this:
browserify client.js | devtool -c
You can also mix Node modules with browser APIs, such as Canvas and WebGL. See example/streetview.js and the respective script in package.json, which grabs a StreetView panorama with some Google Client APIs and writes the PNG image to
For this, you may want to use the
--browser-field flag so that modules like nets will use Web APIs where possible.
devtool street.js --index street.html --quit --bf > street.png
Note: For the output to drain correctly, we need to close the window after the buffer has been written.
See extract-streetview for a practical implementation of this idea built on
-- to avoid any argument conflicts.
# same as "gulp watch"devtool node_modules/gulp/bin/gulp.js -c -- watch# same as "grunt"devtool node_modules/grunt-cli/bin/grunt -c --# run a mocha testdevtool node_modules/mocha/bin/_mocha -qc -- ./tests/my-spec.js
- example/markdown.js - Pipes a
process.stdin, then renders GitHub Flavored Markdown to a PNG image
- example/es2015.js - ES2015 transpiling
- example/geolocate.js - prints current
[ latitude, longitude ]to
- example/http.js - a simple Node.js server that you can throw break points into
Also see devtool-examples for more ideas.
This is built on Electron, so it includes the Console, Profile, Debugger, etc.
It also includes some additional features on top of Electron:
- Improved error handling (more detailed syntax errors in console)
- Improved source map support for required files
- Makes various Node features behave as expected, like
- Console redirection back to terminal (optional)
- File watching for development and quit-on-error flags for unit testing (e.g. continuous integration)
process.exitand error codes
"browser"field resolution (optional)
- Can hide browser globals (like
navigator) for better compatibility with Node.js modules (optional)
- Supports config files for V8 flags, color themes, and other options
Since this is running in Electron and Chromium, instead of Node, you might run into some oddities and gotchas.
windowand other browser APIs are present; this may affect modules using these globals to detect Browser/Node environments
--no-browser-globalsmay help mitigate these issues
- You must call
window.close()to stop the process; apps will not quit on their own
- If a native module does not work, you may need to rebuild it for the right version of Electron
- If you want to close or exit after writing to stderr/stdout, you should do so after a callback:
setIntervaland related functions are shimmed for better compatibility with Node.js
process.stdindoes not work in Windows shells, see this Electron issue
Roadmap / Contributing
This project is experimental and has not been tested on a wide range of applications or Node/OS environments. If you want to help, please open an issue or submit a PR. Some outstanding areas to explore:
- Improving syntax error handling, e.g. adding it to Sources panel
- Exposing an API for programmatic usage
- Exploring native addons
- Testing against a wide range of Node.js applications and modules
git clone and
npm install this repo to start working from source. Type
npm run to list all available commands.
See Also / Comparisons
If you like this, you might also like hihat. It is very similar, but more focused on running and testing browser applications. Hihat uses browserify to bundle everything into a single source file, and uses watchify for incremental file changes.
In some ways,
devtool is a spiritual successor to
hihat. The architecture is cleaner and better suited for large Node/Electron applications.
Another Electron-based debugger is iron-node.
iron-node includes better support for native addons and a complex graphical interface that shows your
devtool is more focused on the command-line, Unix-style piping/redirection, and Electron/Browser APIs for interesting use-cases (e.g. Google StreetView).
devtool shims various features to behave more like Node.js (like
process.exit) and overrides the internal
require mechanism for source maps, improved error handling and
"browser" field resolution.
You may also like node-inspector, which uses remote debugging instead of building on top of Electron.
This means your code will run in a true Node environment, without any
window or other Browser/Electron APIs that may pollute scope and cause problems with certain modules. It has stronger support for large Node.js applications (i.e. native addons) and more control over the DevTools instance (i.e. can inject breakpoints and support Network requests).
However, since it re-implements much of the debugging experience, it may feel clunky and fragile compared to developing inside the latest Chrome DevTools (e.g.
console.profile() does not exist).
devtool aims to make the experience feel more familiar to those coming from Chrome DevTools, and also promotes other features like Browser/Electron APIs.
MIT, see LICENSE.md for details.