replace nulls in props from Rails with undefined

[MaySoMusician]

Summary

closes: discussion #1272

I'm currently working a Rails+React project and eliminating nulls from the type definitions in the frontend as possible, since my team members and I have been bothered about differentiation between null and undefined in terms of typing.

This PR adds an opt-in option to make react_ujs replace all nulls in the props from Rails with undefineds, alongside the option system to allow to selectively enable each option. I've made the option default to false so that all existing projects won't break.

Read the discussion for the more detailed background.

Other Information

As soon as this gets merged, I'll also update @types/react_ujs to add type definitions of setOptions(option)

Pull Request checklist

• Add/update test to cover these changes
• Update documentation
• Update CHANGELOG file

[justin808]

First, there are no tests for this. However, we don't want to change the code.

See my comment in #1272

Let's convert this to a doc PR. I suggest we add a /docs directory.

[MaySoMusician]

@justin808
Replied you in #1272 (reply in thread). Unfortunately I won't still discard my original PR.

[justin808]

@MaySoMusician We now have an app for integration tests. Can you please add tests to https://github.com/reactjs/react-rails/tree/master/test/dummy for your feature and I will merge. Be sure to provide a changelog and readme update.

Thank you for your contribution!

[justin808]

@MaySoMusician can you please add tests.

[MaySoMusician]

@justin808 Sure! I will do that.

[justin808]

@ahangarha Let's get this merged once there are tests.

@MaySoMusician Thanks!

[MaySoMusician]

@justin808 I'll be dealing with this today. Thanks for waiting for me!

[ahangarha]

I recommend naming react_ujs/src/options.js as optionsHelpers.js because it contains only helper functions. The current name options.js suggests having a file with some class or object related to various options.

[ahangarha]

@MaySoMusician Any update?
Please rebase your branch so that your PR can trigger the automated tests.

[justin808]

@MaySoMusician Do you want to finish this one?

[ahangarha]

@justin808 @MaySoMusician I will take the lead so we can go for RC.

[MaySoMusician]

Sorry for my long inactivity. I have encountered so large changes in my employment relationship in recent weeks that I was unable to tackle this. I can have a time to start this tonight, that will take some time since I have to build a vm to install Python2 required by the test environments, which is not installed in recent laptops. @ahangarha @justin808

[ahangarha]

@MaySoMusician Happy to hear from your side.
And I hope that the change in your career ends in your favor.

I think we can wait for a day or two. Looking forward to the update.

[justin808]

We're about to release v3...

[ahangarha]

@MaySoMusician I rebased your changes on the master branch.

[ahangarha]

@MaySoMusician Back to this PR?

[MaySoMusician]

@ahangarha Probably, yes.
And I will try to set up test environment again. #1297 might help me.