Block traversal to global method instances

pointer.ts

@@ -72,8 +72,10 @@ export class Pointer {
       if (key == '__proto__' || key == 'constructor' || key == 'prototype') {
         continue
       }
-      // not sure if this the best way to handle non-existant paths...
-      value = (parent || {})[key]
+      value = undefined
+      if (parent && Object.prototype.hasOwnProperty.call(parent, key)) {
+        value = parent[key]
+      }
     }
     return {parent, key, value}
   }

test/issues.ts

@@ -280,3 +280,12 @@ test('minimal array diff', t => {
   ]
   checkRoundtrip(t, input, output, expected_patch)
 })
+
+test('issues/2ndopp', t => {
+  t.true(({} as any).polluted === undefined, 'toString function should not be polluted')
+  const value = {}
+  applyPatch(value, [
+    {op: 'add', path: '/toString/polluted', value: 'Hello!'}
+  ])
+  t.true(({} as any).toString.polluted === undefined, 'toString function should still not be polluted')
+})