JSI - Create a function that is backed by a jsi::HostObject?

[AndyBrown91]

JSI - Create a function that is backed by a jsi::HostObject?

[neildhar]

Hey @AndyBrown91, have you considered using an ordinary JavaScript function instead of a jsi::HostObject? You can populate your accessors as getters/setters on the function. Note that these getters or setters could be jsi::HostFunctions that update state on the native side associated with the object.

If you need to store data on the native side, you can attach a jsi::NativeState to any JS object (including functions), and access it from your HostFunctions. In general, keeping properties you want to use from JS directly in JS, instead of accessing them through HostObjects is preferable, since accessing JS properties is much more efficient, and reduces the risk of creating uncollectable cycles through jsi::Values.

[AndyBrown91]

Thanks so much for your reply @neildhar

I'm not able to see a way to link a jsi::HostFunction with those property semantics though. Am I missing something?
I felt like the HostObject was the only way to map a C++ getter to a whatever.myprop

The reason why I ask for this stuff is to ensure that it will match the semantics for your linked classes if you use a different JS engine

Maybes there is some magic JS stuff that I have missed for mapping property getters to functions within JS?

[neildhar]

You can use Object.defineProperty to set an arbitrary function (including a HostFunction) as a getter. Loosely, Object.defineProperty(whatever, "myprop", {get: myHF, ...<other flags>}).

[AndyBrown91]

Was just in the process of editing the above, thanks for pointing that out. I'll absolutely give that a go
Really appreciate you helping me reframe the issue

[mikehuebner]

Just chiming in on this, noticed that typeof function is returning object only within production builds.

[neildhar]

@mikehuebner have you observed a bug with Hermes in typeof? Could you open a new issue with the details and a minimal repro?