Load translations with promise, to allow loading before app is initialized

Author: baso10

src/http-loader.ts

@@ -1,7 +1,10 @@
 import {HttpClient} from "@angular/common/http";
 import {TranslateLoader} from "@ngx-translate/core";
+import {Observable} from 'rxjs/Rx';
 
 export class TranslateHttpLoader implements TranslateLoader {
+    loadedTranslations: { [index: string]: Object; } = {};
+
     constructor(private http: HttpClient, public prefix: string = "/assets/i18n/", public suffix: string = ".json") {}
 
     /**
@@ -10,6 +13,27 @@ export class TranslateHttpLoader implements TranslateLoader {
      * @returns {any}
      */
     public getTranslation(lang: string): any {
-        return this.http.get(`${this.prefix}${lang}${this.suffix}`);
+        if (this.loadedTranslations != null && this.loadedTranslations[lang] != null) {
+            return Observable.of(this.loadedTranslations[lang]);
+        }
+        return Observable.fromPromise(this.preLoad(lang));
+    }
+
+    /**
+     * Gets the translations from the server as Promise
+     * @param lang
+     * @returns Promise<any>
+     */
+    public preLoad(lang: string): Promise<any> {
+        return new Promise((resolve, reject) => {
+                this.http.get(`${this.prefix}${lang}${this.suffix}`)
+            .catch((error: any): any => {
+                resolve(null);
+            })
+            .subscribe((result) => {
+                this.loadedTranslations[lang] = result;
+                resolve(result);
+            });
+        });
     }
 }