Updated alert component

Author: cornflourblue

.gitignore

@@ -39,4 +39,7 @@ typings
 
 # Generated files
 app/**/*.js
-app/**/*.js.map
+app/**/*.js.map
+
+# VS Code settings
+.vscode

app/_directives/alert.component.ts

@@ -1,4 +1,5 @@
-import { Component, OnInit } from '@angular/core';
+import { Component, OnDestroy } from '@angular/core';
+import { Subscription } from 'rxjs/Subscription';
 
 import { AlertService } from '../_services/index';
 
@@ -8,12 +9,17 @@ import { AlertService } from '../_services/index';
     templateUrl: 'alert.component.html'
 })
 
-export class AlertComponent {
+export class AlertComponent implements OnDestroy {
+    private subscription: Subscription;
     message: any;
 
-    constructor(private alertService: AlertService) { }
+    constructor(private alertService: AlertService) { 
+        // subscribe to alert messages
+        this.subscription = alertService.getMessage().subscribe(message => { this.message = message; });
+    }
 
-    ngOnInit() {
-        this.alertService.getMessage().subscribe(message => { this.message = message; });
+    ngOnDestroy(): void {
+        // unsubscribe on destroy to prevent memory leaks
+        this.subscription.unsubscribe();
     }
 }