Default value for process.env.NODE_ENV

[davidturissini]

Description

Building an app with observable-membrane as a dependency throws because process.env.NODE_ENV is not defined. In order to fix this, developer has to add rollup-plugin-replace or another tool that will strip out process.env.NODE_ENV. We should provide a default value so that installing this package doesn't immediately break builds.

Steps to Reproduce

1. Start new app with rollup
2. Install observable-membrane
3. Build

Expected Results

No Error 🎉

Actual Results

Uncaught ReferenceError: process is not defined 😿

[pmdartus]

IMO process.env.NODE_ENV should stay in the generated esm modules. Providing a default value means that the bundle can't do dead-code elimination.

Popular libraries like React, Redux or Vue or ship process.env.NODE_ENV in their generated lib and rely on bundler to inject the right values. While rollup requires a plugin, it's done by default by Webpack and browserify. The only format where it makes sense to strip it is for UMD.