Bridged functions taking goja.Value args misbehave around null values

[liclac]

A function that takes a goja.Value argument will, when bridged to JS and invoked with null for that argument, receive a nil goja.Value, which is not recognised as a proper null by goja.IsNull().

Test case:

func TestNullArguments(t *testing.T) {
	rt := goja.New()
	rt.Set("fn", func(v goja.Value) {
		if v == nil {
			t.Error("null becomes nil")
		}
		if !goja.IsNull(v) {
			t.Error("null is not null")
		}
	})
	rt.RunString(`fn(null);`)
}

[dop251]

I have fixed this, however if your function already takes goja.Value as an argument you should consider making it a 'native' goja function. This way you avoid reflection wrapper which will improve performance:

func BenchmarkCallReflect(b *testing.B) {
	vm := New()
	vm.Set("f", func(v Value) {

	})

	prg := MustCompile("test.js", "f(null)", true)

	b.ResetTimer()
	for i := 0; i < b.N; i++ {
		vm.RunProgram(prg)
	}
}

func BenchmarkCallNative(b *testing.B) {
	vm := New()
	vm.Set("f", func(call FunctionCall) (ret Value) {
		return
	})

	prg := MustCompile("test.js", "f(null)", true)

	b.ResetTimer()
	for i := 0; i < b.N; i++ {
		vm.RunProgram(prg)
	}
}

BenchmarkCallReflect-8   	  300000	      4018 ns/op	     160 B/op	       3 allocs/op
BenchmarkCallNative-8    	 2000000	       598 ns/op	     128 B/op	       2 allocs/op