js.ValueOf for an error

[Will Hawkins]

Hello everyone!

First, thank you *all* (I mean this great community) for the Go language and especially its support for a wasm target.

As I was attempting to finish up a CL (https://go-review.googlesource.com/c/go/+/458395) I found occasion to need to great a JS Error based on a Go error. I was hoping to use the JS Error constructor that includes an option object to specify a cause and value (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error/cause) by using the actual go error. Here's what I was thinking:

readErrCause := js.Global().Get("Object").New()

readErrCause.Set("code", readErr.Error())

readErrCause.Set("value", js.ValueOf(readErr))

readErr := js.Global().Get("Error").New("ReadFull failed", readErrCause)

(where readErr is of the `error` type, of course)

Unfortunately,

readErrCause.Set("value", js.ValueOf(readErr))

does not work because, as the comment so perfectly says, ValueOf

// Panics if x is not one of the expected types.

I am absolutely up for proposing and implementing a small addition to the "js package" if people think it would be helpful but I wanted to check here first.

Again, thank you for all the great work that you *all* do!!

Sincerely,

Will

[Brian Candler]

I don't know how a raw Go interface value would be usable in Javascript.  As an alternative, would it be any good to use sprintf("%T", readErr) as the code, and readErr.Error() as the value? At least those are both strings.

https://go.dev/play/p/nd1FXUvD_zg

[Will Hawkins]

I agree. That is what I settled on, basically. Thanks for the suggestion!

Will

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