Allow sw-precache CLI to read config from package.json

[jeffposnick]

It's a common practice supported by other build tools with CLIs, e.g. eslint.

[addyosmani]

Given we support --config=path/to/sw-precache-config.json, do you feel it would make sense to support just a single place for config (either package.json or the external json file) or is the goal short-term to try supporting both?

[jeffposnick]

I don't know. 😦

I'm not happy with the current approach to option parsing in the CLI in general (see #120) and I'm thinking of taking a survery of some major build tools with CLIs (browserify, webpack, eslint, etc.) and see if there's a canonical dependency or pattern that they all use for reading and parsing options.

I'm personally happy with --config, but maybe there's a strong use case for package.json as an additional option? I'd like to research more and am open to feedback!

[addyosmani]

Looking at a few popular CLI tools:

create-react-app seems to use minimist under the hood (we do too via meow): https://github.com/facebookincubator/create-react-app/blob/master/global-cli/index.js#L43

Webpack seems to use https://www.npmjs.com/package/yargs

ESLint seems to use opinionator: https://github.com/gkz/optionator (I've never used this before)

[sindresorhus]

Many tools use pkg-conf to read config from package.json. It's much nicer to be able to specify config in package.json than having to supply CLI flags on every run or creating a npm run script just to persist the flags.

[jeffposnick]

We've started explicitly recommending using objects exposed via module.exports from a standalone JS file for external configuration. I prefer that approach, since there are configuration options that take values which aren't easy to express when serialized to JSON.