Handle JS null values within Ruby code

[richardboehme]

Hey, thanks for providing those great NPM packages!

I'm currently experimenting with writing DOM-Interaction using the JS interoperability module that this package provides. I wonder if it's possible to handle null values with the JS module?

I try to read from localStorage and if a key was not set localStorage.getItem will return null. This null value gets wrapped into a JS::Object which isn't really useful because all reflection methods complain that null is not an object. Could we return nil instead or add a method to JS::Object to identify it being null?

My example:

null_value = JS::global[:localStorage].call('getItem', 'foobar')
p null_value.inspect
# => Uncaught TypeError: Cannot read properties of null (reading 'toString')

I'm happy to help, just not sure how we should approach this.

[kateinoigakukun]

Thank you for reporting!
I think there are 2 topics in your comment.

1. Inspection against null causes TypeError: Cannot read properties of null
2. Implicit conversion from JS null to Ruby nil

The first one is apparently a bug in this library. I've made a patch to fix it. I hope it will solve it.

The second one is a little bit difficult topic around API design. I'm happy to introduce such a conversion in the future, but I'm not confident about its design. For example, if null is implicitly converted into nil, then what should we do for undefined?
It would be longer discussion, so I would like to focus on the 1. bug in this ticket. Feel free to open another issue to discuss the design choice if you want.

[richardboehme]

Thank you for coming back and fixing inspect! I think we also have to add null-checks to other methods. For example JS::Object#call would throw if the object is null.

I'm going to open a discussion about the second point you mentioned!

[richardboehme]

(Started a discussion in #26)

[kateinoigakukun]

Thank you for coming back and fixing inspect! I think we also have to add null-checks to other methods. For example JS::Object#call would throw if the object is null.

Hmm, I think it's expected behavior. What the expected behavior when calling method where the receiver is null?

[richardboehme]

Hmm, I think it's expected behavior. What the expected behavior when calling method where the receiver is null?

Hm you may be right. Maybe I was just confused from the error message at first:

null_value = JS::eval('return null')
null_value.call('foobar')
# Uncaught TypeError: Reflect.get called on non-object

Maybe the idea would be to improve the error message? Maybe it's not necessary though.

[kateinoigakukun]

Ah, I see. It makes sense to stop using Reflect.get to improve error message.