[RRFC] Development lifecycle scripts (hooks)

Motivation ("The Why")

Sometimes in a project, there is a need to setup the development environment or enforce some policies on dependencies used in the project. However, npm doesn't provide a way to hook into its process and lifecycle scripts such as postinstall are (ab)used:

• husky uses postinstall to autoinstall Git hooks and pinst to disable them in the production
• postinstall-postinstall runs the app's postinstall script during its postinstall script
• TBA

Furthermore, there is no way to run a script if the dependency tree of the pakcage has changed, i.e., a dependency is added or removed.

Example

As mentioned above, it can be used to setup the development environment or enforce some policies on dependencies used in the project.

How

Current Behaviour

• postinstall script runs after npm install, but also runs when the package is installed as a dependency
• prepare script runs after npm install, but also before the pakcage is packed
• Both scripts don't run when the dependency tree is changed and there is no way to trigger a script in this case

Desired Behaviour

• A new lifecycle, such as preinstalldep and postinstalldep
• or, hook scripts that run before and after the dependency tree has changed (reify)

References

• Old RFC #34 exists but seems stalled
• Alternative to #325
• Related to #437

Other package managers

• Yarn 1: undocumented hooks can wrap each step (https://github.com/yarnpkg/yarn/pull/7557)
• Yarn 2: hooks can be added via a plugin (https://yarnpkg.com/advanced/plugin-tutorial#using-hooks)
• pnpm: hooks can be added via configuration (https://pnpm.io/pnpmfile)

No implementation files or tests are identified in the issue. Start by reviewing the Current Behaviour, Desired Behaviour, and referenced RFCs #34, #325, and #437; the work is complete when a specific lifecycle-hook design has been agreed and documented.