fix(TranslateService): compile translations only once (#956)

Fixes #955

Author: saithis

projects/ngx-translate/core/src/lib/translate.service.ts

@@ -238,18 +238,23 @@ export class TranslateService {
    */
   public getTranslation(lang: string): Observable<any> {
     this.pending = true;
-    this.loadingTranslations = this.currentLoader.getTranslation(lang).pipe(share());
-
-    this.loadingTranslations.pipe(take(1))
+    const loadingTranslations = this.currentLoader.getTranslation(lang).pipe(share());
+    this.loadingTranslations = loadingTranslations.pipe(
+      take(1),
+      map((res: Object) => this.compiler.compileTranslations(res, lang)),
+      share()
+    );
+
+    this.loadingTranslations
       .subscribe((res: Object) => {
-        this.translations[lang] = this.compiler.compileTranslations(res, lang);
+        this.translations[lang] = res;
         this.updateLangs();
         this.pending = false;
       }, (err: any) => {
         this.pending = false;
       });
 
-    return this.loadingTranslations;
+    return loadingTranslations;
   }
 
   /**
@@ -369,7 +374,7 @@ export class TranslateService {
           observer.error(err);
         };
         this.loadingTranslations.subscribe((res: any) => {
-          res = this.getParsedResult(this.compiler.compileTranslations(res, this.currentLang), key, interpolateParams);
+          res = this.getParsedResult(res, key, interpolateParams);
           if (typeof res.subscribe === "function") {
             res.subscribe(onComplete, onError);
           } else {

projects/ngx-translate/core/tests/translate.service.spec.ts

@@ -406,4 +406,30 @@ describe('TranslateService', () => {
 
     expect(getTranslationCalls).toEqual(1);
   }));
+
+  it('should compile translations only once, even when subscribing to translations while translations are loading', fakeAsync(() => {
+    spyOn(translate.currentLoader, 'getTranslation').and.callFake(() => {
+      return timer(1000).pipe(mapTo(of(translations)));
+    });
+
+    let translateCompilerCallCount = 0;
+    spyOn(translate.compiler, 'compile').and.callFake((value) => {
+      ++translateCompilerCallCount;
+      return value;
+    });
+    spyOn(translate.compiler, 'compileTranslations').and.callFake((value) => {
+      ++translateCompilerCallCount;
+      return value;
+    });
+
+    translate.setDefaultLang('en-US');
+    translate.get('TEST1').subscribe();
+    translate.get('TEST2').subscribe();
+    translate.get('TEST3').subscribe();
+    translate.get('TEST4').subscribe();
+
+    tick(1001);
+
+    expect(translateCompilerCallCount).toBe(1);
+  }));
 });