From ce1fcea68c7d5e0249c6c1c1fc612a86b2866243 Mon Sep 17 00:00:00 2001
From: Manu MA <manu.valladolid@gmail.com>
Date: Wed, 21 Nov 2018 23:59:12 +0100
Subject: [PATCH] fix(angular): es6 classes break in ie11 (#16417)

fixes #15979
---
 angular/src/providers/platform.ts | 19 +++++++++----------
 1 file changed, 9 insertions(+), 10 deletions(-)

diff --git a/angular/src/providers/platform.ts b/angular/src/providers/platform.ts
index d6be8c8da9..564664bb00 100644
--- a/angular/src/providers/platform.ts
+++ b/angular/src/providers/platform.ts
@@ -3,15 +3,8 @@ import { BackButtonDetail, Platforms, getPlatforms, isPlatform } from '@ionic/co
 import { proxyEvent } from '../util/util';
 
 
-export class BackButtonEmitter extends EventEmitter<BackButtonDetail> {
-  constructor() {
-    super();
-  }
-  subscribeWithPriority(priority: number, callback: () => Promise<any> | void) {
-    return this.subscribe((ev: BackButtonDetail) => {
-      ev.register(priority, callback);
-    });
-  }
+export interface BackButtonEmitter extends EventEmitter<BackButtonDetail> {
+  subscribeWithPriority(priority: number, callback: () => Promise<any> | void): void;
 }
 
 @Injectable()
@@ -22,7 +15,7 @@ export class Platform {
   /**
    * @hidden
    */
-  backButton = new BackButtonEmitter();
+  backButton: BackButtonEmitter = new EventEmitter<BackButtonDetail>() as any;
 
   /**
    * The pause event emits when the native platform puts the application
@@ -47,6 +40,12 @@ export class Platform {
   resize = new EventEmitter<void>();
 
   constructor() {
+    this.backButton.subscribeWithPriority = function(priority, callback) {
+      return this.subscribe((ev: BackButtonDetail) => {
+        ev.register(priority, callback);
+      });
+    };
+
     proxyEvent(this.pause, document, 'pause');
     proxyEvent(this.resume, document, 'resume');
     proxyEvent(this.backButton, document, 'ionBackButton');