The `Puppeteer` class had two concerns:
* connect to an existing browser
* launch a new browser
The first of those concerns is needed in all environments, but the
second is only needed in Node.
https://github.com/puppeteer/puppeteer/pull/6484 landing enabled us to
pull the `Puppeteer` class apart into two:
1. `Puppeteer` which hosts the behaviour for connecting to existing
browsers.
2. `PuppeteerNode`, which extends `Puppeteer` and also adds the ability
to launch a new browser.
This is a non-breaking change, because Node users will still get an
instance of a class with all the methods they expect, but it'll be a
`PuppeteerNode` rather than `Puppeteer`. I don't expect this to cause
people any issues.
We also now have new files that are effectively the entry points for
Puppeteer:
* `node.ts`: the main entry point for Puppeteer on Node.
* `web.ts`: the main entry point for Puppeteer on the web.
* `node-puppeteer-core.ts`: for those using puppeteer-core (which only
exists in Node, not on the web).
* chore: vendor Mitt into src/common/third-party
As discussed in #6203 we need to vendor our common dependencies in so
that when we ship an ESM build all imports point to file paths and do
not rely on Node resolution (e.g. a browser does not understand `import
mitt from 'mitt'`).
* chore(agnostic): ship CJS and ESM builds
For our work to enable Puppeteer in other environments (e.g. a browser)
we need to ship an ESM build. This commit changes our config to ship to
`lib/cjs` and `lib/esm` accordingly. The majority of our code stays the
same, with one small fix for the CJS build to ensure that we ship a
version that lets you `require('puppeteer')` rather than have to
`require('puppeteer').default`. We do this with the `cjs-entry.js` which
is what the `main` field in our `package.json` points to.
We also swap to `read-pkg-up` to find the `package.json` file. This is
because the folder structure of `lib/` does not match `src/` now we ship
to `cjs` and `esm`, so you cannot rely on exact paths. This module works
up from the file to find the nearest `package.json` so it will always
find Puppeteer's `package.json`.
Note that we *do not* point any users to the ESM build. We happen to
ship those files so people who know about them can get at them but it's
not expected (nor will we actively support) that people will rely on
them. The CommonJS build is considered our main build.
We may make breaking changes to the structure of the ESM build which we
will do without requiring new major versions. For example the ESM build
currently ships all files that the CJS build does, but given we are
working on the ESM build being able to run in the browser this may
change over time.
Long term once the Node versions catch up we can ditch CJS and ship
exclusively ESM but we are not there yet.
