fix(core): use bind of the cloned object for enumerable getter

src/core/json-schema/src/formly-json-schema.service.ts

@@ -182,20 +182,21 @@ export class FormlyJsonschema {
 
         // TODO: remove isEnum check once adding an option to skip extension
         if (!this.isEnum(schema)) {
+          const _this = this;
           Object.defineProperty(field, 'fieldArray', {
-            get: () => {
+            get: function() {
               if (!Array.isArray(schema.items)) {
                 // When items is a single schema, the additionalItems keyword is meaningless, and it should not be used.
-                return this._toFieldConfig(<JSONSchema7> schema.items, options);
+                return _this._toFieldConfig(<JSONSchema7> schema.items, options);
               }
 
-              const length = field.fieldGroup ? field.fieldGroup.length : 0;
+              const length = this.fieldGroup ? this.fieldGroup.length : 0;
               const itemSchema = schema.items[length]
                 ? schema.items[length]
                 : schema.additionalItems;
 
               return itemSchema
-                ? this._toFieldConfig(<JSONSchema7> itemSchema, options)
+                ? _this._toFieldConfig(<JSONSchema7> itemSchema, options)
                 : {};
             },
             enumerable: true,

src/core/src/lib/utils.spec.ts

@@ -196,4 +196,13 @@ describe('clone', () => {
     expect(propDescriptor.get).toBeDefined();
     expect(propDescriptor.enumerable).toBeTruthy();
   });
+
+  it('should use bind of the cloned object', () => {
+    const d = {};
+    Object.defineProperty(d, 'a', { get: function() { return this.name; }, enumerable: true });
+    const value = clone(d);
+    value.name = 'foo';
+
+    expect(value.a).toEqual('foo');
+  });
 });

src/core/src/lib/utils.ts

@@ -132,10 +132,9 @@ export function clone(value: any): any {
   // need to make a deep copy so we dont use Object.assign
   // also Object.assign wont copy property descriptor exactly
   return Object.keys(value).reduce((newVal, prop) => {
-    const propDescriptor = Object.getOwnPropertyDescriptor(value, prop);
-
-    if (propDescriptor.get) {
-      Object.defineProperty(newVal, prop, { ...propDescriptor, get: () => clone(value[prop]) });
+    const propDesc = Object.getOwnPropertyDescriptor(value, prop);
+    if (propDesc.get) {
+      Object.defineProperty(newVal, prop, propDesc);
     } else {
       newVal[prop] = clone(value[prop]);
     }