refactor custom isEqual to utilise lodash.isequal

packages/apollo-utilities/package.json

@@ -40,7 +40,11 @@
   },
   "dependencies": {
     "fast-json-stable-stringify": "^2.0.0",
+    "lodash.isequal": "^4.5.0",
     "ts-invariant": "^0.4.0",
     "tslib": "^1.9.3"
+  },
+  "devDependencies": {
+    "@types/lodash.isequal": "^4.5.5"
   }
 }

packages/apollo-utilities/src/util/__tests__/isEqual.ts

@@ -90,4 +90,85 @@ describe('isEqual', () => {
     expect(!isEqual([1, 2, 3], [1, 2, 4])).toBe(true);
     delete Array.prototype.foo;
   });
+
+  describe('comparing objects with circular refs', () => {
+    // copied with slight modification from lodash test suite
+    it('should compare objects with circular references', () => {
+      const object1 = {},
+        object2 = {};
+
+      object1.a = object1;
+      object2.a = object2;
+
+      expect(isEqual(object1, object2)).toBe(true);
+
+      object1.b = 0;
+      object2.b = Object(0);
+
+      expect(isEqual(object1, object2)).toBe(true);
+
+      object1.c = Object(1);
+      object2.c = Object(2);
+
+      expect(isEqual(object1, object2)).toBe(false);
+
+      object1 = { a: 1, b: 2, c: 3 };
+      object1.b = object1;
+      object2 = { a: 1, b: { a: 1, b: 2, c: 3 }, c: 3 };
+
+      expect(isEqual(object1, object2)).toBe(false);
+    });
+
+    it('should have transitive equivalence for circular references of objects', () => {
+      const object1 = {},
+        object2 = { a: object1 },
+        object3 = { a: object2 };
+
+      object1.a = object1;
+
+      expect(isEqual(object1, object2)).toBe(true);
+      expect(isEqual(object2, object3)).toBe(true);
+      expect(isEqual(object1, object3)).toBe(true);
+    });
+
+    it('should compare objects with multiple circular references', () => {
+      const array1 = [{}],
+        array2 = [{}];
+
+      (array1[0].a = array1).push(array1);
+      (array2[0].a = array2).push(array2);
+
+      expect(isEqual(array1, array2)).toBe(true);
+
+      array1[0].b = 0;
+      array2[0].b = Object(0);
+
+      expect(isEqual(array1, array2)).toBe(true);
+
+      array1[0].c = Object(1);
+      array2[0].c = Object(2);
+
+      expect(isEqual(array1, array2)).toBe(false);
+    });
+
+    it('should compare objects with complex circular references', () => {
+      const object1 = {
+        foo: { b: { c: { d: {} } } },
+        bar: { a: 2 },
+      };
+
+      const object2 = {
+        foo: { b: { c: { d: {} } } },
+        bar: { a: 2 },
+      };
+
+      object1.foo.b.c.d = object1;
+      object1.bar.b = object1.foo.b;
+
+      object2.foo.b.c.d = object2;
+      object2.bar.b = object2.foo.b;
+
+      expect(isEqual(object1, object2)).toBe(true);
+    });
+  });
 });

packages/apollo-utilities/src/util/isEqual.ts

@@ -1,47 +1,8 @@
+import isEqualLodash from 'lodash.isequal';
+
 /**
  * Performs a deep equality check on two JavaScript values.
  */
 export function isEqual(a: any, b: any): boolean {
-  // If the two values are strictly equal, we are good.
-  if (a === b) {
-    return true;
-  }
-  // Dates are equivalent if their time values are equal.
-  if (a instanceof Date && b instanceof Date) {
-    return a.getTime() === b.getTime();
-  }
-  // If a and b are both objects, we will compare their properties. This will compare arrays as
-  // well.
-  if (
-    a != null &&
-    typeof a === 'object' &&
-    b != null &&
-    typeof b === 'object'
-  ) {
-    // Compare all of the keys in `a`. If one of the keys has a different value, or that key does
-    // not exist in `b` return false immediately.
-    for (const key in a) {
-      if (Object.prototype.hasOwnProperty.call(a, key)) {
-        if (!Object.prototype.hasOwnProperty.call(b, key)) {
-          return false;
-        }
-        if (!isEqual(a[key], b[key])) {
-          return false;
-        }
-      }
-    }
-    // Look through all the keys in `b`. If `b` has a key that `a` does not, return false.
-    for (const key in b) {
-      if (
-        Object.prototype.hasOwnProperty.call(b, key) &&
-        !Object.prototype.hasOwnProperty.call(a, key)
-      ) {
-        return false;
-      }
-    }
-    // If we made it this far the objects are equal!
-    return true;
-  }
-  // Otherwise the values are not equal.
-  return false;
+  return isEqualLodash(a, b);
 }