[feat] Allow environment variables definition when launching chromium

[BenoitZugmeyer]

I'd like to launch Chromium with a specific timezone for my tests. On Linux and macOS, I just need to define the TZ environment variable to the wanted timezone. So I added a new puppeteer.launch() option to allow defining the environment variables of the forked process.

I read the contributing rules, but I failed to write a good unit test for Windows, because Chromium seems to ignore the TZ environment variable on this platform. If anyone have an idea for a more cross-platform unit test, I'd be happy to amend my PR. For now, the test is simply disabled on Windows.

FWIW, a similar issue is open at the chrome-launcher project.

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[BenoitZugmeyer]

I signed it!

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[aslushnikov]

Hi @BenoitZugmeyer, thank you for the pull request.

The code looks legit. However, I wonder if setting up process.env prior to launching browser would work for your use case?

const savedEnv = Object.assign({}, process.env);

process.env.TZ = 'America/Noronha';
const browser = await puppeteer.launch();

Object.assign(process.env, savedEnv); // Restore env

[BenoitZugmeyer]

It is indeed possible to mutate the process.env, but I find it inconvenient for one major reason: In your code sample, since you are restoring the environment after waiting for puppeteer.launch to finish, the env is altered for any concurrent task going on. A better (but more inconvenent) solution would be:

const savedEnv = Object.assign({}, process.env);

process.env.TZ = 'America/Noronha';
const browserPromise = puppeteer.launch();
Object.assign(process.env, savedEnv); // Restore env

const browser = await browserPromise;

This is possible because puppeteer.launch is calling child_process.spawn synchronously.

Also, in my opinion, documenting the possibility to define the chromium environment variables this way is clearer than letting the user guess how to do it by mutating process.env.

[aslushnikov]

Lets not add this test - it adds more debt.
The patch is small and mostly does plumbing, so we can tolerate landing this without a test.

[BenoitZugmeyer]

Alright, test removed! (commit amended)

[chux0519]

Why setting the time zone to "Asia/Shanghai" does not work, and eventually I use 'utc-8' instead？