Export returns wrong Go value for a JS "undefined" value about otto HOT 2 CLOSED

Oh, the output of the test looks like:

        value = otto.Value{_valueType:1, value:interface {}(nil)}
        value = otto.Value{_valueType:2, value:interface {}(nil)}
        Expected nil, got otto.Value{_valueType:2, value:interface {}(nil)}

from otto.

undefined is kind of a weird case, because it's not technically null.

In addition, I see the Export function as a sort of "best-effort" export. That is, try and export this ECMA value to something closer to Go, but if not, just return the otto.Value, since that is still a valid Go type/value.

So, theoretically, the best representation of an undefined value (which is entirely an ECMA concept) in Go is as an otto.Value.

That being said, I'm gonna take a page from JSON.stringify and consider Export to be like a JSON export. You can see this reasoning in more detail in section 15.12.3 of the ECMA-262 specification.

An undefined value in an array is represented by null (nil).
An undefined value in an object causes that property to not exist in the exported result.

Caveat: The two rules above are good, and should not change, but exporting an undefined value by itself is undefined, and could change in the future. For now, it will export nil.

from otto.