fix(decorator): do not override props with same name

Now every property is stored on it's own object instance that is hidden from enumeration

Author: gund

__tests__/decorator.ts

@@ -1,4 +1,4 @@
-import { EMPTY, Subject } from 'rxjs';
+import { EMPTY, Observable, Subject } from 'rxjs';
 
 import { WithUntilDestroyed } from '../src/decorator';
 import * as untilDestroyedObj from '../src/take-until-destroy';
@@ -58,4 +58,18 @@ describe('@WithUntilDestroyed decorator', () => {
 
     expect(callback).not.toHaveBeenCalled();
   });
+
+  it('should not share value between instances', () => {
+    class Test {
+      @WithUntilDestroyed()
+      stream$ = new Observable();
+
+      ngOnDestroy() {}
+    }
+
+    const t1 = new Test();
+    const t2 = new Test();
+
+    expect(t1.stream$).not.toBe(t2.stream$);
+  });
 });

src/decorator.ts

@@ -21,19 +21,22 @@ import { untilDestroyed } from './take-until-destroy';
  *
  * Do not forget to implement {@link OnDestroy} life-cycle hook.
  */
-export function WithUntilDestroyed(
-  destroyMethodName?: string,
-): PropertyDecorator {
-  return (target, propKey) => {
-    let val: Observable<any>;
+export function WithUntilDestroyed(destroyMethodName?: string): PropertyDecorator {
+  return function(target, propKey) {
+    const valKey = `__WithUntilDestroyed:${String(propKey)}__`;
 
     function getter() {
-      return val;
+      return this[valKey];
     }
 
     function setter(newVal) {
       if (isObservable(newVal)) {
-        val = newVal.pipe(untilDestroyed(this, destroyMethodName));
+        delete this[valKey];
+        Object.defineProperty(this, valKey, {
+          configurable: true,
+          enumerable: false,
+          value: newVal.pipe(untilDestroyed(this, destroyMethodName)),
+        });
       } else {
         throw Error(
           `WithUntilDestroyed: Property ${String(propKey)} on ${