Support Object.create(null) in JSON diffing

src/diff/json.js

@@ -1,9 +1,6 @@
 import Diff from './base';
 import {lineDiff} from './line';
 
-const objectPrototypeToString = Object.prototype.toString;
-
-
 export const jsonDiff = new Diff();
 // Discriminate between two lines of pretty-printed, serialized JSON where one of them has a
 // dangling comma and the other doesn't. Turns out including the dangling comma yields the nicest output:
@@ -41,7 +38,7 @@ export function canonicalize(obj, stack, replacementStack, replacer, key) {
 
   let canonicalizedObj;
 
-  if ('[object Array]' === objectPrototypeToString.call(obj)) {
+  if ('[object Array]' === Object.prototype.toString.call(obj)) {
     stack.push(obj);
     canonicalizedObj = new Array(obj.length);
     replacementStack.push(canonicalizedObj);
@@ -65,7 +62,7 @@ export function canonicalize(obj, stack, replacementStack, replacer, key) {
         key;
     for (key in obj) {
       /* istanbul ignore else */
-      if (obj.hasOwnProperty(key)) {
+      if (Object.prototype.hasOwnProperty.call(obj, key)) {
         sortedKeys.push(key);
       }
     }

test/diff/json.js

@@ -182,6 +182,22 @@ describe('diff/json', function() {
         { count: 1, value: '}', removed: false, added: false }
       ]);
     });
+
+    it("doesn't throw on Object.create(null)", function() {
+      let diff;
+      expect(function() {
+        diff = diffJson(
+          Object.assign(Object.create(null), {a: 123}),
+          {b: 456}
+        );
+      }).not.to['throw']();
+      expect(diff).to.eql([
+        { count: 1, value: '{\n', removed: false, added: false },
+        { count: 1, value: '  \"a\": 123\n', removed: true, added: false },
+        { count: 1, value: '  \"b\": 456\n', removed: false, added: true },
+        { count: 1, value: '}', removed: false, added: false }
+      ]);
+    });
   });
 });