Fix inconsistent field names in javascript plugin hooks (#4869)

pkg/javascript/vm.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"net/http"
 	"os"
+	"reflect"
 
 	"github.com/dop251/goja"
 )
@@ -16,8 +17,27 @@ type VM struct {
 	GQLHandler    http.Handler
 }
 
+// optionalFieldNameMapper wraps a goja.FieldNameMapper and returns the field name if the wrapped mapper returns an empty string.
+type optionalFieldNameMapper struct {
+	mapper goja.FieldNameMapper
+}
+
+func (tfm optionalFieldNameMapper) FieldName(t reflect.Type, f reflect.StructField) string {
+	if ret := tfm.mapper.FieldName(t, f); ret != "" {
+		return ret
+	}
+
+	return f.Name
+}
+
+func (tfm optionalFieldNameMapper) MethodName(t reflect.Type, m reflect.Method) string {
+	return tfm.mapper.MethodName(t, m)
+}
+
 func NewVM() *VM {
-	return &VM{Runtime: goja.New()}
+	r := goja.New()
+	r.SetFieldNameMapper(optionalFieldNameMapper{goja.TagFieldNameMapper("json", true)})
+	return &VM{Runtime: r}
 }
 
 type APIAdder interface {