Support JSON stats output

[billyjanitsch]

• Operating System: macOS 10.13.4
• Node Version: 10.0.0
• NPM Version: 6.0.0
• webpack Version: 4.8.1
• webpack-command Version: 0.2.0

This issue is for a:

• bug
• feature request
• modification request

Code

CLI Command

  $ webpack --json

webpack.config.js

n/a

Expected Behavior

webpack-cli (and formerly the bundled webpack CLI) has a --json arg which causes the stats to be printed out as JSON. This is extremely useful for piping into files which can then be uploaded to web-based bundle analysis tools.

It would be great if webpack-command could support this flag or something equivalent -- perhaps through a reporter. Since webpack-command is already working with the JSON stats, I assume this would be a low-overhead feature to support.

I'm about to take a vacation but I might be able to get a PR out before I leave if this sounds reasonable to you.

Actual Behavior

There is currently no way to get the build stats as JSON.

New Feature Use Case

See expected behavior above.

[shellscape]

@billyjanitsch thanks for the issue 🍺

This is exactly why we have the ability to write custom reporters. (And if you get one working that you like, and you think would be useful, it could be submitted for inclusion by default). I'd use the BasicReporter as a template for that.

[billyjanitsch]

Cool. I will PR a JSON reporter either before or after my vacation.

These lines will be a problem because there is no way to disable them, and it's important that this reporter print only a single valid JSON object. Do you mind if I change the internals to allow the reporter to disable all other output, or is there a better option?

[shellscape]

You can actually pull some trickery with that log object. In the constructor for your reporter:

this.log = weblog({ name: 'webpack', id: 'webpack-command' });
this.setLogLevel = log.logLevel;
log.logLevel = 'silent';

And then in the render method for your reporter, restore the level:

this.log.logLevel = this.setLogLevel;

Though I'm not sure if that's needed, especially if your reporter is only intended to report JSON and nothing more. Something else to consider: writing the JSON output to stderr so you can still allow the logging as per usual, but then could redirect stderr to a file or for examination by another process. That'd be the best of both worlds.

[valscion]

Something else to consider: writing the JSON output to stderr so you can still allow the logging as per usual, but then could redirect stderr to a file or for examination by another process. That'd be the best of both worlds.

Could we instead do the opposite? If I'm not mistaken, it's common practice to log informational output to stderr if stdout will be used for e.g. piping.

Here's one nice blog post summarizing what I've understood stderr and stdout should be used for: https://www.jstorimer.com/blogs/workingwithcode/7766119-when-to-use-stderr-instead-of-stdout

[shellscape]

@valscion welcome to the nuances of writing tooling in the webpack ecosystem: no matter how many considerations you make for how people are going to work with a thing, someone will always have another method they're asking to account for 😄

There hasn't been a huge demand for this yet, so I really have no preference for how this functions. No one has stepped up to provide this in a PR yet.

[valscion]

I hope my comment wasn't coming through as assertative. Didn't mean to bring bad feelings. (I feel the need to apologise as your reply comes off a bit snarky, and I worry it's my fault)

Anyway. Great to hear that either way goes ☺️. I'm in the process of painfully migrating to webpack 4 and wanted to use webpack-command, and as I'm maintaining webpack-bundle-analyzer, having the --json flag supported here would be useful to allow for the CLI usage of webpack-bundle-analyzer.

I might get to writing this JSON reporter, depending on how much energy this migration will end up consuming 😅

[shellscape]

I hope my comment wasn't coming through as assertative. Didn't mean to bring bad feelings. (I feel the need to apologise as your reply comes off a bit snarky, and I worry it's my fault)

Tangent: I believe people anymore are way too worried about the mere possibility of offending someone. My reply contained no snark, it was straight truth. And it even had a smiley face. If your reply offended anyone, they can go jump in a lake, because it was absolutely fine and perfectly illustrated the nuances I mentioned.