Define environment variables by default

[silverwind]

I think it'd make sense to define everything in process.env by default, so instead of

/// #if env == 'PRODUCTION'
/// #if PRODUCTION

one can do a more standard

/// #if NODE_ENV === 'production'
/// #if process.env.NODE_ENV === 'production'

Variables defined in options should overwrite bare variables like NODE_ENV but process.env should always reflect the actual environment.

I imagine this would allow to integrate the loader with default options in most cases.

[yoursunny]

Caution: on Windows, there are default environment variable names that contain ( character, such as ProgramFiles(x86).
If they are defined as part of options by default, it will cause error on this line:

ifdef-loader/preprocessor.ts

Line 209 in 5018e64

const f = new Function(...args, code);

See kenpb/parcel-plugin-ifdef#2 for more information.