Can you elaborate this a bit? How would this work?

If I run a node project without now dev, I can specify that I want to open a debugger which I can interact with. It would be great to be able to pass something to now dev that would allow me to do something similar. Example command without now dev is something like this: node --inspect -r ts-node/register ./src/index.ts

Ahh, I see. Thanks @mckernanin.

This sounds like something we could make happen at the config-level (in now.json).

This would make the debugging workflow so much easier, really need this!

Progress?

I got so far as to get the VSCode debugging tools to launch now dev, with lambdas working as expected, with the following launch.json:

{
  // Use IntelliSense to learn about possible attributes.
  // Hover to view descriptions of existing attributes.
  // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
  "version": "0.2.0",
  "configurations": [
    {
      "type": "node",
      "request": "launch",
      "name": "Launch Now Dev",
      "program": "/home/nick/.yarn/bin/now",
      "args": ["dev"]
    }
  ]
}

To set up on your machine, replace /home/nick/.yarn/bin/now with the location of your globally-installed now executable.

At least 2 problems remain:

1. What I can't figure out (probably because of my lack of experience with debugging using VSCode) is how to actually get the debugging features to work. As in, set breakpoints in the lambdas accessible through the routes defined in my now.json, and have those breakpoints get caught when running those lambdas through now dev.

2. Just going by the error codes that I'm getting, it looks like there might be an issue with source maps, causing an exception, albeit one which doesn't prevent the development server from running. Here's the Debug Console output from VSCode:

/home/nick/.nvm/versions/node/v12.8.0/bin/node --inspect-brk=19993 ../../../../.yarn/bin/now dev 
Debugger listening on ws://127.0.0.1:19993/40ef08d3-4140-43e0-8d7a-b6d7a04d04a7
For help, see: https://nodejs.org/en/docs/inspector
Debugger attached.
SourceMaps.getMapForGeneratedPath: exception while processing path: /home/nick/.config/yarn/global/node_modules/now/dist/index.js, sourcemap: index.js.map
TypeError: Cannot create property 'sourceRoot' on string '{"version":3,"sources":["/webpack/bootstrap","../.ent/node_modules/async-sema/lib/index.js","../home/runner/work/now/now/node_modules/generic-pool/lib/Pool.js","../home/runner/work/now/now/node_modules/@zeit/fun/node_modules/tar/lib/update.js","../node_modules/node-fetch/lib/request.js","../home/runner/work/now/now/node_modules/@sentry/node/dist/version.js","../home/runner/work/now/now/node_modules/inquirer/node_modules/ansi-regex/index.js","../home/runner/work/now/now/node_modules/asynckit/serialOrdered.js","../external \"domain\"","../home/runner/work/now/now/node_modules/source-map-resolve/lib/resolve-url.js","../home/runner/work/now/now/node_modules/stripe/lib/stripe.js","../home/runner/work/now/now/node_modules/bluebird/js/release/each.js","../src/util/output/elapsed.ts","../home/runner/work/now/now/node_modules/psl/index.js","../home/runner/work/now/now/node_modules/stream-to-promise/node_modules/once/once.js","../home/runner/work/now/now/node_modules/download/node_modules/content-disposition/index.js","../home/runner/work/now/now/node_modules/ecc-jsbn/index.js","../home/runner/work/now/now/node_modules/sshpk/lib/key.js","../home/runner/work/now/now/node_modules/@sentry/utils/dist/logger.js","../home/runner/work/now/now/node_modules/minipass/index.js","../home/[...]

> Now CLI 16.3.1 dev (beta) — https://zeit.co/feedback/dev
> Ready! Available at http://localhost:3000

System and Versions

Linux x64 (Pop_OS! 19.10)
Now 16.3.1
Visual Studio Code 1.39.2

Now dev would need to expose access to the debugger enabled node process.

_{Sent with GitHawk}

Sorry @NWRichmond, we can't debug a program launched by another process (now). It is possible if now dev adds a flag to set debug and port options.

This is important, I'm looking at a way of doing this when running my Next.js app from my local computer.

Found a hacky way that is documented on #2077

And this issue should be closed in favour of the other one

It could be better to add some mechanism to add any flag to underlying node instance --inspect or any other flag with now-cli.

@leo I don't think that now.json is the right place because you probably want to activate it only through a yarn/npm command like yarn dev:inspect.
The main reason why you don't want to have this inspect mode always activated (with your config file), is because it can conflict with the default listening port, if you have another node process with inspection enabled. If we choose this config file way to activate it then we need to let user choose a port number.

It would be easier to only add a --inspect option to now-cli but I don't think it would be relevant for other platform than node.

I would happy to help because I am migrating my API from now v1 to v2 and loosing this debug capability is a real blocker.

Desperately want this!

Thank you for creating this issue!

Please note that – in order for us to be able to handle each feature request with care – we have to consume all of them through a unified pipeline that makes it easier for us to prioritize, track and progress on the features our user base is interested in.

In turn, the Issues tab on this repository is best only be used for reporting bugs, which we can immediately act on.

For well-explained feature requests (like the one you just posted), please contact us at support@zeit.co, so that we can consider adding it to our roadmap.

As asked, I wrote to the support team and will update this thread if anything new comes up. (even though it's closed)

@Vadorequest are there any news about this issue? I'd like to use webstorm debugger but haven't found a way yet

I haven't had any feedback from the support team at this time.

install now locally and then

node --inspect node_modules/.bin/now dev

but the break point doesn't work, vscode says: "Breakpoint ignored because generated code not found (source map problem?)"

@gaoxiaoliangz this is the exact issue found with Webstorm debugger. I can start the debugger or run the code but the breakpoints doesn't work at all.

I currently use the following steps to debug my code on the local vercel instance using vscode:

1. Start the local vercel server using vercel dev.
2. Go to the vscode debug tab ctrl + shift + d.
3. Create a launch.json file using the create a launch.json file button.
4. Chose node.js option from the dropdown menu.
5. Add another configuration using the Add Configuration button.
6. Choose node.js: Attach to process option from the dropdown menu.
7. Set a breakpoint.
8. Start the Attach by Process ID debug session.
9. See that the debugger works.

Hope this helps somebody.

Still struggling with trying to get the vscode debugger to work on a next app with vercel dev.. This is such a disjointed experience. I cannot set a breakpoint in vscode.

@offero Strange, I have the breakpoints working on my side (see system info below) . I however noticed that on firefox sometimes the breakpoints are skipped. Did you try chrome?

Version: 1.62.3
Commit: ccbaa2d27e38e5afa3e5c21c1c7bef4657064247
Date: 2021-11-17T08:00:36.721Z
Electron: 13.5.2
Chrome: 91.0.4472.164
Node.js: 14.16.0
V8: 9.1.269.39-electron.0
OS: Linux x64 5.11.0-38-generic

I got vscode to debug with vercel dev.

In your package.json, create any script name (eg: "start:local": "vercel dev").
Click on a break point that you want your code to stop at a specific API route.
Hover over the "start:local" and run as: "Debug Script". Call that API route and it should hit that endpoint with your data.