From b7decfd1551e735213e2e64445ca4ece3d059a40 Mon Sep 17 00:00:00 2001
From: Michael Best <mbest@dasya.com>
Date: Tue, 17 Oct 2017 11:22:09 -0700
Subject: [PATCH] Make sure a null afterRender doesn't fail + add some tests

---
 spec/bindingAttributeBehaviors.js     |  5 +++++
 spec/bindingDependencyBehaviors.js    | 32 +++++++++++++++++++++++++++
 src/binding/bindingAttributeSyntax.js | 15 ++++++++-----
 3 files changed, 46 insertions(+), 6 deletions(-)

diff --git a/spec/bindingAttributeBehaviors.js b/spec/bindingAttributeBehaviors.js
index 1291c53ab..9504ccef3 100644
--- a/spec/bindingAttributeBehaviors.js
+++ b/spec/bindingAttributeBehaviors.js
@@ -621,4 +621,9 @@ describe('Binding attribute syntax', function() {
         ko.applyBindings({ callback: function () { callbacks++; } }, testNode);
         expect(callbacks).toEqual(0);
     });
+
+    it('Should ignore (and not throw an error) for a null afterRender callback', function () {
+        testNode.innerHTML = "<div data-bind='afterRender: null'><span data-bind='text: \"Some Text\"'></span></div>";
+        ko.applyBindings({}, testNode);
+    });
 });
diff --git a/spec/bindingDependencyBehaviors.js b/spec/bindingDependencyBehaviors.js
index 1fa714ab0..4d5513fef 100644
--- a/spec/bindingDependencyBehaviors.js
+++ b/spec/bindingDependencyBehaviors.js
@@ -289,6 +289,38 @@ describe('Binding dependencies', function() {
         expect(callbacks).toEqual(2);
     });
 
+    it('Should always use the latest value of an afterRender callback', function () {
+        ko.bindingHandlers.test = {
+            init: function() {
+                return { controlsDescendantBindings: true };
+            },
+            update: function(element, valueAccessor, allBindings, viewModel, bindingContext) {
+                var innerContext = bindingContext.createChildContext({childprop: ko.utils.unwrapObservable(valueAccessor())});
+                element.innerHTML = "<span data-bind='text: childprop'></span>";
+                ko.applyBindingsToDescendants(innerContext, element);
+            }
+        };
+
+        var callbackSpy1 = jasmine.createSpy('callbackSpy1'),
+            callbackSpy2 = jasmine.createSpy('callbackSpy2'),
+            vm = {
+                observable: ko.observable('value'),
+                callback: callbackSpy1
+            };
+
+        testNode.innerHTML = "<div data-bind='test: observable, afterRender: callback'></div>";
+        ko.applyBindings(vm, testNode);
+        expect(callbackSpy1).toHaveBeenCalled();
+
+        callbackSpy1.reset();
+        vm.callback = callbackSpy2;
+
+        vm.observable('new value');
+        expect(testNode.childNodes[0]).toContainText('new value');
+        expect(callbackSpy1).not.toHaveBeenCalled();
+        expect(callbackSpy2).toHaveBeenCalled();
+    });
+
     describe('Observable view models', function() {
         it('Should update bindings (including callbacks)', function() {
             var vm = ko.observable(), clickedVM;
diff --git a/src/binding/bindingAttributeSyntax.js b/src/binding/bindingAttributeSyntax.js
index 72a3c27d6..acb95fc9d 100755
--- a/src/binding/bindingAttributeSyntax.js
+++ b/src/binding/bindingAttributeSyntax.js
@@ -235,12 +235,15 @@
 
             var afterRender = ko.utils.domData.get(elementOrVirtualElement, afterRenderCallbackDomDataKey);
             if (afterRender) {
-                var nodes = ko.virtualElements.childNodes(elementOrVirtualElement);
-                if (nodes.length) {
-                    ko.dependencyDetection.ignore(function () {
-                        evaluateValueAccessor(afterRender)(nodes, ko.dataFor(nodes[0]));
-                    });
-                }
+                ko.dependencyDetection.ignore(function () {
+                    afterRender = evaluateValueAccessor(afterRender);
+                    if (afterRender) {
+                        var nodes = ko.virtualElements.childNodes(elementOrVirtualElement);
+                        if (nodes.length) {
+                            afterRender(nodes, ko.dataFor(nodes[0]));
+                        }
+                    }
+                });
             }
         }
     }