fix(TS): Error impls now properly type this (#4978)

Fixes an issue with TypeScript compilation in more strict environments.

src/internal/util/ArgumentOutOfRangeError.ts

@@ -6,7 +6,7 @@ export interface ArgumentOutOfRangeErrorCtor {
 }
 
 const ArgumentOutOfRangeErrorImpl = (() => {
-  function ArgumentOutOfRangeErrorImpl(this: any) {
+  function ArgumentOutOfRangeErrorImpl(this: Error) {
     Error.call(this);
     this.message = 'argument out of range';
     this.name = 'ArgumentOutOfRangeError';

src/internal/util/EmptyError.ts

@@ -6,7 +6,7 @@ export interface EmptyErrorCtor {
 }
 
 const EmptyErrorImpl = (() => {
-  function EmptyErrorImpl(this: any) {
+  function EmptyErrorImpl(this: Error) {
     Error.call(this);
     this.message = 'no elements in sequence';
     this.name = 'EmptyError';

src/internal/util/ObjectUnsubscribedError.ts

@@ -6,7 +6,7 @@ export interface ObjectUnsubscribedErrorCtor {
 }
 
 const ObjectUnsubscribedErrorImpl = (() => {
-  function ObjectUnsubscribedErrorImpl(this: any) {
+  function ObjectUnsubscribedErrorImpl(this: Error) {
     Error.call(this);
     this.message = 'object unsubscribed';
     this.name = 'ObjectUnsubscribedError';

src/internal/util/TimeoutError.ts

@@ -6,7 +6,7 @@ export interface TimeoutErrorCtor {
 }
 
 const TimeoutErrorImpl = (() => {
-  function TimeoutErrorImpl(this: any) {
+  function TimeoutErrorImpl(this: Error) {
     Error.call(this);
     this.message = 'Timeout has occurred';
     this.name = 'TimeoutError';

src/internal/util/UnsubscriptionError.ts

@@ -7,13 +7,13 @@ export interface UnsubscriptionErrorCtor {
 }
 
 const UnsubscriptionErrorImpl = (() => {
-  function UnsubscriptionErrorImpl(this: any, errors: any[]) {
+  function UnsubscriptionErrorImpl(this: Error, errors: (Error|string)[]) {
     Error.call(this);
     this.message = errors ?
       `${errors.length} errors occurred during unsubscription:
 ${errors.map((err, i) => `${i + 1}) ${err.toString()}`).join('\n  ')}` : '';
     this.name = 'UnsubscriptionError';
-    this.errors = errors;
+    (this as any).errors = errors;
     return this;
   }
 
@@ -26,4 +26,4 @@ ${errors.map((err, i) => `${i + 1}) ${err.toString()}`).join('\n  ')}` : '';
  * An error thrown when one or more errors have occurred during the
  * `unsubscribe` of a {@link Subscription}.
  */
-export const UnsubscriptionError: UnsubscriptionErrorCtor = UnsubscriptionErrorImpl as any;
+export const UnsubscriptionError: UnsubscriptionErrorCtor = UnsubscriptionErrorImpl as any;