This may or may not be a "bug" per se, but attempting to call a method on a nil interface results in a JS error, rather than a GopherJS runtime error. Example:

package main

func main() {
	foo := GetFoo()
	foo.Foo()
}

type Foo interface {
	Foo()
}

func GetFoo() Foo {
	return nil
}

Results in:

TypeError: foo.Foo is not a function

Or in Chrome:

main.js:146674 Uncaught TypeError: Cannot read property 'Foo' of undefined

This is only undesirable insofar as it tends to suggest a problem with a JS lib.

In Go the same error is reported as:

panic: runtime error: invalid memory address or nil pointer dereference

Something similar would be ideal, IMHO, in GopherJS.