feat(preloader): preloader service which can take a list of promises and execute smth once all promises are completed

src/app/theme/services/baImageLoader/index.ts

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+export * from './baImageLoader.service.ts';

src/app/theme/services/baThemePreloader/baThemePreloader.service.ts

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+import {Injectable} from '@angular/core';
+
+@Injectable()
+export class BaThemePreloader {
+
+  private static _loaders:Array<Promise<any>> = [];
+
+  public static registerLoader(method:Promise<any>):void {
+    BaThemePreloader._loaders.push(method);
+  }
+
+  public static clear():void {
+    BaThemePreloader._loaders = [];
+  }
+
+  public static load():Promise<any> {
+    return new Promise((resolve, reject) => {
+      BaThemePreloader._executeAll(resolve);
+    });
+  }
+
+  private static _executeAll(done:Function):void {
+    setTimeout(() => {
+      Promise.all(BaThemePreloader._loaders).then((values) => {
+        done.call(null, values);
+
+      }).catch((error) => {
+        console.error(error);
+      });
+    });
+  }
+}

src/app/theme/services/baThemePreloader/index.ts

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+export * from './baThemePreloader.service.ts';

src/app/theme/services/index.ts

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+export * from './baImageLoader';
+export * from './baThemePreloader';