toJSON checks for Realm.Object or Realm.Collection before calling toJ…

…SON recursively.

lib/extensions.js

@@ -82,7 +82,8 @@ module.exports = function(realmConstructor, context) {
 
     Object.defineProperty(realmConstructor.Collection.prototype, "toJSON", {
         value: function (_, cache = new Map()) {
-            return this.map((item, index) => item.toJSON ? item.toJSON(index.toString(), cache) : item);
+            return this.map((item, index) =>
+                item instanceof realmConstructor.Object ? item.toJSON(index.toString(), cache) : item);
         },
 
         writable: true,
@@ -112,8 +113,10 @@ module.exports = function(realmConstructor, context) {
             Object.keys(this)
                 .concat(Object.keys(Object.getPrototypeOf(this)))
                 .forEach(key => {
-                    // TODO: check that we're dealing with a Realm type, before passing in cache?
-                    result[key] = this[key].toJSON ? this[key].toJSON(key, cache) : this[key];
+                    const value = this[key];
+                    result[key] = value instanceof realmConstructor.Object || value instanceof realmConstructor.Collection
+                        ? value.toJSON(key, cache)
+                        : value;
                 });
 
             return result;