get rid of warning during build an linting

src/app/group-monitor/booklet.service.ts

@@ -2,7 +2,6 @@ import {Injectable} from '@angular/core';
 import {MainDataService} from '../maindata.service';
 import {BackendService} from './backend.service';
 import {Observable, of} from 'rxjs';
-import {isDefined} from '@angular/compiler/src/util';
 import {map, shareReplay} from 'rxjs/operators';
 import {Booklet, BookletError, BookletMetadata, Restrictions, Testlet, Unit} from './group-monitor.interfaces';
 import {BookletConfig} from '../config/booklet-config';
@@ -11,49 +10,14 @@ import {BookletConfig} from '../config/booklet-config';
 @Injectable()
 export class BookletService {
 
-
     public booklets: Observable<Booklet|BookletError>[] = [];
 
-
     constructor(
         private bs: BackendService
     ) { }
 
-
-    public getBooklet(bookletName: string): Observable<Booklet|BookletError> {
-
-        if (isDefined(this.booklets[bookletName])) {
-
-            // console.log('FORWARDING booklet for ' + bookletName + '');
-            return this.booklets[bookletName];
-        }
-
-        if (bookletName == "") {
-
-            // console.log("EMPTY bookletID");
-            this.booklets[bookletName] = of<Booklet|BookletError>({error: 'missing-id'});
-
-        } else {
-
-            // console.log('LOADING testletOrUnit data for ' + bookletName + ' not available. loading');
-
-            this.booklets[bookletName] = this.bs.getBooklet(bookletName)
-                .pipe(
-                    map((response: string|BookletError) => {
-                        return (typeof response === 'string') ? BookletService.parseBookletXml(response) : response;
-                    }),
-                    shareReplay(1)
-                );
-        }
-
-        return this.booklets[bookletName];
-    }
-
-
     private static parseBookletXml(xmlString: string): Booklet|BookletError {
-
         try {
-
             const domParser = new DOMParser();
             const bookletElement = domParser.parseFromString(xmlString, 'text/xml').documentElement;
 
@@ -67,17 +31,13 @@ export class BookletService {
                 metadata: BookletService.parseMetadata(bookletElement),
                 config: BookletService.parseBookletConfig(bookletElement)
             };
-
         } catch (error) {
-
             console.warn('Error reading booklet XML:', error);
             return {error: 'xml'};
         }
     }
 
-
     private static parseBookletConfig(bookletElement: Element): BookletConfig {
-
         const bookletConfigElements = BookletService.xmlGetChildIfExists(bookletElement, 'BookletConfig', true);
         const bookletConfig = new BookletConfig();
         bookletConfig.setFromKeyValuePairs(MainDataService.getTestConfig());
@@ -87,23 +47,17 @@ export class BookletService {
         return bookletConfig;
     }
 
-
     private static parseMetadata(bookletElement: Element): BookletMetadata {
-
         const metadataElement = BookletService.xmlGetChildIfExists(bookletElement, 'Metadata');
-
         return {
-            id: BookletService.xmlGetChildTextIfExists(metadataElement, "Id"),
-            label: BookletService.xmlGetChildTextIfExists(metadataElement, "Label"),
-            description: BookletService.xmlGetChildTextIfExists(metadataElement, "Description", true),
-        }
+            id: BookletService.xmlGetChildTextIfExists(metadataElement, 'Id'),
+            label: BookletService.xmlGetChildTextIfExists(metadataElement, 'Label'),
+            description: BookletService.xmlGetChildTextIfExists(metadataElement, 'Description', true),
+        };
     }
 
-
     private static parseTestlet(testletElement: Element): Testlet {
-
         // TODO id will be mandatory (https://github.com/iqb-berlin/testcenter-iqb-php/issues/116), the remove fallback to ''
-
         return {
             id: testletElement.getAttribute('id') || '',
             label:  testletElement.getAttribute('label') || '',
@@ -114,55 +68,40 @@ export class BookletService {
         };
     }
 
-
     private static parseUnitOrTestlet(unitOrTestletElement: Element): (Unit|Testlet) {
-
-        if (unitOrTestletElement.tagName == 'Unit') {
+        if (unitOrTestletElement.tagName === 'Unit') {
             return {
                 id: unitOrTestletElement.getAttribute('alias') || unitOrTestletElement.getAttribute('id'),
                 label: unitOrTestletElement.getAttribute('label'),
                 labelShort: unitOrTestletElement.getAttribute('labelshort')
-            }
+            };
         }
-
         return BookletService.parseTestlet(unitOrTestletElement);
     }
 
-
     private static parseRestrictions(testletElement: Element): Restrictions {
-
         const restrictions: Restrictions = {};
-
         const restrictionsElement = BookletService.xmlGetChildIfExists(testletElement, 'Restrictions', true);
-
         if (!restrictionsElement) {
-
             return restrictions;
         }
-
         const codeToEnterElement = restrictionsElement.querySelector('CodeToEnter');
         if (codeToEnterElement) {
-
             restrictions.codeToEnter = {
                 code: codeToEnterElement.getAttribute('code'),
                 message: codeToEnterElement.textContent
-            }
+            };
         }
-
         const timeMaxElement = restrictionsElement.querySelector('TimeMax');
         if (timeMaxElement) {
-
             restrictions.timeMax = {
                 minutes: parseFloat(timeMaxElement.getAttribute('minutes')),
             };
         }
-
         return restrictions;
     }
 
-
     private static xmlGetChildIfExists(element: Element, childName: string, isOptional: boolean = false): Element {
-
         const elements = BookletService.xmlGetDirectChildrenByTagName(element, [childName]);
         if (!elements.length && !isOptional) {
             throw new Error(`Missing field: '${childName}'`);
@@ -170,26 +109,42 @@ export class BookletService {
         return elements.length ? elements[0] : null;
     }
 
-
-    private static xmlGetChildTextIfExists(element: Element, childName: string, isOptional: boolean = false) : string {
-
+    private static xmlGetChildTextIfExists(element: Element, childName: string, isOptional: boolean = false): string {
         const childElement = BookletService.xmlGetChildIfExists(element, childName, isOptional);
-        return childElement ? childElement.textContent : "";
+        return childElement ? childElement.textContent : '';
     }
 
-
     private static xmlGetDirectChildrenByTagName(element: Element, tagNames: string[]): Element[] {
-
         return [].slice.call(element.childNodes)
-            .filter((element: Element) => (element.nodeType === 1))
-            .filter((element: Element) => (tagNames.indexOf(element.tagName) > -1));
+            .filter((elem: Element) => (elem.nodeType === 1))
+            .filter((elem: Element) => (tagNames.indexOf(elem.tagName) > -1));
     }
 
-
     private static xmlCountChildrenOfTagNames(element: Element, tagNames: string[]): number {
-
         return element.querySelectorAll(tagNames.join(', ')).length;
     }
+
+    public getBooklet(bookletName: string): Observable<Booklet|BookletError> {
+        if (typeof this.booklets[bookletName] !== 'undefined') {
+            // console.log('FORWARDING booklet for ' + bookletName + '');
+            return this.booklets[bookletName];
+        }
+        if (bookletName === '') {
+            // console.log("EMPTY bookletID");
+            this.booklets[bookletName] = of<Booklet|BookletError>({error: 'missing-id'});
+
+        } else {
+            // console.log('LOADING testletOrUnit data for ' + bookletName + ' not available. loading');
+            this.booklets[bookletName] = this.bs.getBooklet(bookletName)
+                .pipe(
+                    map((response: string|BookletError) => {
+                        return (typeof response === 'string') ? BookletService.parseBookletXml(response) : response;
+                    }),
+                    shareReplay(1)
+                );
+        }
+        return this.booklets[bookletName];
+    }
 }