Expose isEquals escape hatch

index.js

@@ -33,6 +33,7 @@ function newContext() {
   update.extend = function(directive, fn) {
     commands[directive] = fn;
   };
+  update.isEquals = function(a, b) { return a === b; };
 
   return update;
 
@@ -58,10 +59,14 @@ function newContext() {
     var index, key;
     getAllKeys(spec).forEach(function(key) {
       if (hasOwnProperty.call(commands, key)) {
+        var objectWasNextObject = object === nextObject;
         nextObject = commands[key](spec[key], nextObject, spec, object);
+        if (objectWasNextObject && update.isEquals(nextObject, object)) {
+          nextObject = object;
+        }
       } else {
         var nextValueForKey = update(object[key], spec[key]);
-        if (nextValueForKey !== nextObject[key]) {
+        if (!update.isEquals(nextValueForKey, nextObject[key])) {
           if (nextObject === object) {
             nextObject = copy(object);
           }

test.js

@@ -324,11 +324,13 @@ describe('update', function() {
 
 
 describe('update', function() {
+
+  var myUpdate;
+  beforeEach(function() {
+    myUpdate = update.newContext();
+  });
+
   describe('can extend functionality', function() {
-    var myUpdate;
-    beforeEach(function() {
-      myUpdate = update.newContext();
-    });
 
     it('allows adding new directives', function() {
       myUpdate.extend('$addtax', function(tax, original) {
@@ -399,4 +401,17 @@ describe('update', function() {
     expect(update.bind(null, obj, {$merge: {a: 'b'}})).toNotThrow()
   });
 
+  it('supports an escape hatch for isEquals', function() {
+    myUpdate.isEquals = function(a, b) {
+      return JSON.stringify(a) === JSON.stringify(b);
+    }
+    var a = {b: {c: {d: [4, 5]}}};
+    var b = myUpdate(a, {b: {c: {d: {$set: [4, 5]}}}});
+    var c = myUpdate(a, {b: {$set: {c: {d: [4, 5]}}}});
+    var d = myUpdate(a, {$set: {b: {c: {d: [4, 5]}}}});
+    expect(a).toBe(b)
+    expect(a).toBe(c)
+    expect(a).toBe(d)
+  })
+
 });