Watch mode: Allow adding files to watch when using the --watch flag

[gustavnikolaj]

What is the problem this feature will solve?

The new --watch flag will automatically restart the process when any imported file is changed.

The new related --watch-path flag will restart the process when one of the added paths change.

Using --watch-path disables the automatic restarting based on imported modules.

--watch is what you want 99% of the time, but there are cases where you want to extend the watched files ever-so-slightly.

One such example is .env when used with the dotenv module. No matter if you do it programmatically, or through the use of a -r flag to the node process, changes in the .env. file will not trigger a reload.

Other examples could be configuration files in json, yaml og toml formats.

What is the feature you are proposing to solve the problem?

A new flag which will allow extending the set of watched files based on what is imported/required, with specific non-js files which are loaded through non-discoverable methods, without disabling the automatic discovery of files.

The automatic discoverability of files to watch is a killer feature! Unfortunately not being able to add individual files to the watched set is preventing me from using it.

What alternatives have you considered?

I can keep using nodemon or the current --watch-path feature, but have to enumerate and eagerly watch all files that could possibly be loaded. But as --watch-path does not work on Linux it will likely have to be nodemon.

[gustavnikolaj]

cc @MoLow

(I would add the watch-mode label if I had permission to do so)

[aduh95]

Could you illustrate your request with a minimal example? IIUC for the following setup:

echo '{"key": "initial value"}' > file.json
echo 'module.exports = JSON.parse(require("node:fs").readFileSync("./file.json", "utf-8"))' > dep.js
echo 'console.log(require("./dep.js"))' > entry.js
node --watch-path=file.json --watch entry.js

You would like that on top of any change to file.json, any change to dep.js would also restart the process, is that correct? Or are you talking about having a new API, and if so, can you give an example how it could look like?

[gustavnikolaj]

You would like that on top of any change to file.json, any change to dep.js would also restart the process, is that correct?

That illustrates the behavior I'm looking for, correctly!

Some javascript code loads a non-javascript file and use it as input. In my example it is the dotenv package, which when used as node --require dotenv/config ... will load the .env file in the current working directory and populate process.env with the values there. I want changes in the .env file to cause a reload, and I am alright that I have to manually tell node to do so, when it cannot trivially be statically analyzed.

Or are you talking about having a new API, and if so, can you give an example how it could look like?

Honestly, I don't really know. The default behavior of --watch is brilliant. This is how nodemon or all other watch tool should work by default, and why such a tool belongs in core. I was a bit surprised to see that --watch-path implicitly de-activate the behavior of --watch, but I assume that there is a good reason.

--watch-path-but-also-do-not-disable-normal-watch is my naive request, but I am pretty sure that there is a better way. And I'm also pretty sure that I am not the only one with this use case, so I thought I would add the feedback here when I did not find another issue addressing it.

[MoLow]

@gustavnikolaj are you interested in creating a PR to support your use-case?
we can either add a new flag for that, or make --watch-path behave the way it does only in case passed exclusively (i.e without --watch

[umutciloglu]

I'm not really experienced but i can take a look if it's ok.

[MoLow]

Go for it!

[debadree25]

Hello, could you guide me on any supporting documentation or relevant parts of the codebase I could look into?

[debadree25]

Have been attempting to take a stab at this, still unable to find the place where the import logic is written, any pointers would be very helpful
cc @MoLow

Thank You!

[MoLow]

@debadree25 most of the watch mode implementation is in this file: https://github.com/nodejs/node/blob/de696d70ef1d0a5ff52312709914134306bd7c82/lib/internal/main/watch_mode.js

[debadree25]

I tried to run @aduh95 's example curiously I see an empty output, could be doing something wrong, or could this be a bug:

running node v18.11.0 on macOS 13.0.1

[theoephraim]

It may be tricky depending on the implementation, but it could also make sense to let the code programatically add files to the watch list -- which could even reset on each restart to keep things simple.

But that way the file that is deciding where those config files are and their paths can trigger adding them rather than having to modify the way I run the program itself.

[NwaforAugustine321]

@MoLow I want to know if the issue is still open for me to work on it. Thanks and am looking forward to hearing from you

[MoLow]

I am closing this issue - I think #45182 will provide a better solution for this and is now easier to implement