fix(Notification): replace const enum (#4556)

* fix(Notification): replace const enum
Closes#4538
* chore: use literal union and keep enum
The enum is kept, but it is no longer a const enum. It cannot be exported as a const enum without effecting an error if isolated modules are used.

Author: cartant

src/internal/Notification.ts

@@ -3,8 +3,13 @@ import { Observable } from './Observable';
 import{empty}from'./observable/empty';
 import{of}from'./observable/of';
 import{throwError}from'./observable/throwError';
+import{deprecate}from'util';
 
-exportconstenumNotificationKind{
+// TODO: When this enum is removed, replace it with a type alias. See #4556.
+/**
+ * @deprecated NotificationKind is deprecated as const enums are not compatible with isolated modules. Use a string literal instead.
+ */
+exportenumNotificationKind{
 NEXT='N',
 ERROR='E',
 COMPLETE='C',
@@ -27,8 +32,8 @@ export const enum NotificationKind {
 exportclassNotification<T>{
 hasValue: boolean;
 
-constructor(publickind: NotificationKind,publicvalue?: T,publicerror?: any){
-this.hasValue=kind===NotificationKind.NEXT;
+constructor(publickind: 'N'|'E'|'C',publicvalue?: T,publicerror?: any){
+this.hasValue=kind==='N';
 }
 
 /**
@@ -38,11 +43,11 @@ export class Notification<T> {
  */
 observe(observer: PartialObserver<T>): any{
 switch(this.kind){
-caseNotificationKind.NEXT:
+case'N':
 returnobserver.next&&observer.next(this.value);
-caseNotificationKind.ERROR:
+case'E':
 returnobserver.error&&observer.error(this.error);
-caseNotificationKind.COMPLETE:
+case'C':
 returnobserver.complete&&observer.complete();
 }
 }
@@ -58,11 +63,11 @@ export class Notification<T> {
 do(next: (value: T)=>void,error?: (err: any)=>void,complete?: ()=>void): any{
 constkind=this.kind;
 switch(kind){
-caseNotificationKind.NEXT:
+case'N':
 returnnext&&next(this.value);
-caseNotificationKind.ERROR:
+case'E':
 returnerror&&error(this.error);
-caseNotificationKind.COMPLETE:
+case'C':
 returncomplete&&complete();
 }
 }
@@ -92,18 +97,18 @@ export class Notification<T> {
 toObservable(): Observable<T>{
 constkind=this.kind;
 switch(kind){
-caseNotificationKind.NEXT:
+case'N':
 returnof(this.value);
-caseNotificationKind.ERROR:
+case'E':
 returnthrowError(this.error);
-caseNotificationKind.COMPLETE:
+case'C':
 returnempty();
 }
 thrownewError('unexpected notification kind value');
 }
 
-privatestaticcompleteNotification: Notification<any>=newNotification(NotificationKind.COMPLETE);
-privatestaticundefinedValueNotification: Notification<any>=newNotification(NotificationKind.NEXT,undefined);
+privatestaticcompleteNotification: Notification<any>=newNotification('C');
+privatestaticundefinedValueNotification: Notification<any>=newNotification('N',undefined);
 
 /**
  * A shortcut to create a Notification instance of the type `next` from a
@@ -115,7 +120,7 @@ export class Notification<T> {
  */
 staticcreateNext<T>(value: T): Notification<T>{
 if(typeofvalue!=='undefined'){
-returnnewNotification(NotificationKind.NEXT,value);
+returnnewNotification('N',value);
 }
 returnNotification.undefinedValueNotification;
 }
@@ -129,7 +134,7 @@ export class Notification<T> {
  * @nocollapse
  */
 staticcreateError<T>(err?: any): Notification<T>{
-returnnewNotification(NotificationKind.ERROR,undefined,err);
+returnnewNotification('E',undefined,err);
 }
 
 /**