From a32bd19369af81f0b0b2aaf4486188c8670eb1c5 Mon Sep 17 00:00:00 2001
From: Michael Best <mbest@dasya.com>
Date: Sat, 15 Apr 2017 02:13:20 -0700
Subject: [PATCH] Add third parameter to ko.applyBindings for modifying the
 root context

---
 spec/bindingAttributeBehaviors.js     | 21 ++++++++++++++++++---
 src/binding/bindingAttributeSyntax.js |  8 ++++----
 2 files changed, 22 insertions(+), 7 deletions(-)

diff --git a/spec/bindingAttributeBehaviors.js b/spec/bindingAttributeBehaviors.js
index 5393c0874..edf441584 100644
--- a/spec/bindingAttributeBehaviors.js
+++ b/spec/bindingAttributeBehaviors.js
@@ -29,7 +29,7 @@ describe('Binding attribute syntax', function() {
                 didInit = true;
             }
         };
-        testNode.innerHTML = "<div id='testElement' data-bind='test:123'></div>";
+        testNode.innerHTML = "<div id='testElement' data-bind='test'></div>";
         ko.applyBindings(suppliedViewModel);
         expect(didInit).toEqual(true);
     });
@@ -44,10 +44,10 @@ describe('Binding attribute syntax', function() {
                 didInit = true;
             }
         };
-        testNode.innerHTML = "<div id='testElement' data-bind='test:123'></div>";
+        testNode.innerHTML = "<div id='testElement' data-bind='test'></div>";
 
         var shouldNotMatchNode = document.createElement("DIV");
-        shouldNotMatchNode.innerHTML = "<div id='shouldNotMatchThisElement' data-bind='test:123'></div>";
+        shouldNotMatchNode.innerHTML = "<div id='shouldNotMatchThisElement' data-bind='test'></div>";
         document.body.appendChild(shouldNotMatchNode);
         this.after(function () { document.body.removeChild(shouldNotMatchNode); });
 
@@ -55,6 +55,21 @@ describe('Binding attribute syntax', function() {
         expect(didInit).toEqual(true);
     });
 
+    it('applyBindings should accept three parameters and use the third parameter as a callback for modifying the root context', function() {
+        var didInit = false;
+        ko.bindingHandlers.test = {
+            init: function (element, valueAccessor, allBindings, viewModel, bindingContext) {
+                expect(bindingContext.extraValue).toEqual("extra");
+                didInit = true;
+            }
+        };
+        testNode.innerHTML = "<div id='testElement' data-bind='test'></div>";
+        ko.applyBindings(null, testNode, function(context) {
+            context.extraValue = "extra";
+        });
+        expect(didInit).toEqual(true);
+    });
+
     it('Should tolerate empty or only white-space binding strings', function() {
         testNode.innerHTML = "<div data-bind=''></div><div data-bind='   '></div>";
         ko.applyBindings(null, testNode); // No exception means success
diff --git a/src/binding/bindingAttributeSyntax.js b/src/binding/bindingAttributeSyntax.js
index da5b0508f..94445a88a 100755
--- a/src/binding/bindingAttributeSyntax.js
+++ b/src/binding/bindingAttributeSyntax.js
@@ -399,10 +399,10 @@
         return bindingInfo && bindingInfo.context;
     }
 
-    function getBindingContext(viewModelOrBindingContext) {
+    function getBindingContext(viewModelOrBindingContext, extendContextCallback) {
         return viewModelOrBindingContext && (viewModelOrBindingContext instanceof ko.bindingContext)
             ? viewModelOrBindingContext
-            : new ko.bindingContext(viewModelOrBindingContext);
+            : new ko.bindingContext(viewModelOrBindingContext, undefined, undefined, extendContextCallback);
     }
 
     ko.applyBindingAccessorsToNode = function (node, bindings, viewModelOrBindingContext) {
@@ -421,7 +421,7 @@
             applyBindingsToDescendantsInternal(getBindingContext(viewModelOrBindingContext), rootNode, true);
     };
 
-    ko.applyBindings = function (viewModelOrBindingContext, rootNode) {
+    ko.applyBindings = function (viewModelOrBindingContext, rootNode, extendContextCallback) {
         // If jQuery is loaded after Knockout, we won't initially have access to it. So save it here.
         if (!jQueryInstance && window['jQuery']) {
             jQueryInstance = window['jQuery'];
@@ -437,7 +437,7 @@
             throw Error("ko.applyBindings: first parameter should be your view model; second parameter should be a DOM node");
         }
 
-        applyBindingsToNodeAndDescendantsInternal(getBindingContext(viewModelOrBindingContext), rootNode, true);
+        applyBindingsToNodeAndDescendantsInternal(getBindingContext(viewModelOrBindingContext, extendContextCallback), rootNode, true);
     };
 
     // Retrieving binding context from arbitrary nodes