GopherJS's zero value for unsafe.Pointer is a numeric 0 (I'm guessing for interop with uintptr, but not entirely sure). However, this is incompatible with a pointer interface and causes incorrect behavior when converted into another pointer type:

package main

import (
	"unsafe"
)

func main() {
	var up unsafe.Pointer

	p := (*bool)(up)
	if p != nil {
		println("error: p should be nil")
	}
	println("not nil", *p)
}

By contrast, if up is initialized with unsafe.Pointer((*bool)(nil)), the program works correctly.