Copy over acessor properties to target object sinonjs#2387

lib/sinon/util/core/extend.js

@@ -102,13 +102,24 @@ module.exports = function extend(target, ...sources) {
             if (prop === "name" && !destOwnPropertyDescriptor.writable) {
                 return;
             }
-
-            Object.defineProperty(dest, prop, {
+            const descriptors = {
                 configurable: sourceOwnPropertyDescriptor.configurable,
-                enumerable: sourceOwnPropertyDescriptor.enumerable,
-                writable: sourceOwnPropertyDescriptor.writable,
-                value: sourceOwnPropertyDescriptor.value,
-            });
+                enumerable: sourceOwnPropertyDescriptor.enumerable
+            }
+            /*
+                if the sorce has an Accessor property copy over the accessor functions (get and set)
+                data properties has writable attribute where as acessor property don't
+                REF: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#properties
+            */
+
+            if (hasOwnProperty(sourceOwnPropertyDescriptor, 'writable')) {
+                descriptors.writable = sourceOwnPropertyDescriptor.writable
+                descriptors.value = sourceOwnPropertyDescriptor.value
+            } else {
+                if (sourceOwnPropertyDescriptor.get) { descriptors.get = sourceOwnPropertyDescriptor.get.bind(dest) }
+                if (sourceOwnPropertyDescriptor.set) { descriptors.set = sourceOwnPropertyDescriptor.set.bind(dest) }
+            }
+            Object.defineProperty(dest, prop, descriptors);
         }
     );
 };

test/extend-test.js

@@ -78,6 +78,56 @@ describe("extend", function () {
         assert.equals(result, expected);
     });
 
+    it("copies acessor properties into the target", function () {
+        var target = {
+            "hello" : "hello"
+        }
+        const obj = {
+            private: 1
+        }
+        Object.defineProperty(obj, "lexical", {
+            configurable: true,
+            enumerable: true,
+            get: () => this.private,
+            set: value => {
+                this.private = value;
+            }
+        });
+        Object.defineProperty(obj, "instance", {
+            configurable: true,
+            enumerable: true,
+            get: () => obj.private,
+            set: value => {
+                obj.private = value;
+            }
+        });
+        Object.defineProperty(obj, "bound", {
+            configurable: true,
+            enumerable: true,
+            get: function () { return this.private },
+            set: function (value) {
+                this.private = value;
+            }
+        });
+        extend(target, obj);
+        assert.equals(target.hello, "hello")
+        assert.equals(target.lexical === undefined, true)
+        assert.equals(target.instance, 1)
+        assert.equals(target.bound, 1)
+        target.lexical = 2
+        assert.equals(target.lexical, 2)
+        assert.equals(target.instance, 1)
+        assert.equals(target.bound, 1)
+        target.instance = 3
+        assert.equals(target.lexical, 2)
+        assert.equals(target.instance, 3)
+        assert.equals(target.bound, 1)
+        target.bound = 4
+        assert.equals(target.lexical, 2)
+        assert.equals(target.instance, 3)
+        assert.equals(target.bound, 4)
+    })
+
     context("when 'name' property is not writable", function () {
         it("does not attempt to write to the property", function () {
             var object1 = { prop1: null };