錯誤：未捕獲（承諾中）：TypeError：無法讀取未定義的屬性「映射」

僅當它嘗試從catch返回值時，纔會發生以下錯誤。希望我在這裏做一個根本錯誤的事情。請給我一個線索。爲什麼我不能從catch返回observable？錯誤：未捕獲（承諾中）：TypeError：無法讀取未定義的屬性「映射」

.TS

getMyTopic() { 
    return this.topicSer.getMyTopics().map((res: any) => res.json()).map((res: any) => res = res.categories) 
     .catch((err: any) => { 
     console.log('err', err); 
     return [] 
     }) 
    }

provider.ts

getMyTopics(): Observable<any> { 
     if (typeof this.userService.userDetails != 'undefined') { 
      this.localCacheService.getItem(this.localCacheService.discoverTopicsKey).then((val) => { 
     if (val != null && val.length == 0) return this.apiService.get(config.discover_topic_WITHAUTH); 
     }).catch(() => { 
     return this.apiService.get(config.discover_topic_WITHOUTAUTH);//here is the issue 
      }); 
     }

錯誤

ERROR Error: Uncaught (in promise): TypeError: Cannot read property 'map' of undefined 
TypeError: Cannot read property 'map' of undefined 
    at Discover.webpackJsonp.402.Discover.getMyTopic (discover.ts:123) 
    at Discover.webpackJsonp.402.Discover.getData (discover.ts:69) 
    at discover.ts:51 
    at t.invoke (polyfills.js:3) 
    at Object.onInvoke (core.js:4626) 
    at t.invoke (polyfills.js:3) 
    at r.run (polyfills.js:3) 
    at polyfills.js:3 
    at t.invokeTask (polyfills.js:3) 
    at Object.onInvokeTask (core.js:4617) 
    at Discover.webpackJsonp.402.Discover.getMyTopic (discover.ts:123) 
    at Discover.webpackJsonp.402.Discover.getData (discover.ts:69) 
    at discover.ts:51 
    at t.invoke (polyfills.js:3) 
    at Object.onInvoke (core.js:4626) 
    at t.invoke (polyfills.js:3) 
    at r.run (polyfills.js:3) 
    at polyfills.js:3 
    at t.invokeTask (polyfills.js:3) 
    at Object.onInvokeTask (core.js:4617) 
    at c (polyfills.js:3) 
    at polyfills.js:3 
    at t.invokeTask (polyfills.js:3) 
    at Object.onInvokeTask (core.js:4617) 
    at t.invokeTask (polyfills.js:3) 
    at r.runTask (polyfills.js:3) 
    at o (polyfills.js:3) 
    at e.invokeTask [as invoke] (polyfills.js:3) 
    at p (polyfills.js:2) 
    at IDBRequest.v (polyfills.js:2) 
defaultErrorLogger @ core.js:1350 
ErrorHandler.handleError @ core.js:1411 
IonicErrorHandler.handleError @ ionic-error-handler.js:61 
next @ core.js:5373 
schedulerFn @ core.js:4220 
SafeSubscriber.__tryOrUnsub @ Subscriber.js:238 
SafeSubscriber.next @ Subscriber.js:185 
Subscriber._next @ Subscriber.js:125 
Subscriber.next @ Subscriber.js:89 
Subject.next @ Subject.js:55 
EventEmitter.emit @ core.js:4200 
(anonymous) @ core.js:4648 
t.invoke @ polyfills.js:3 
r.run @ polyfills.js:3 
NgZone.runOutsideAngular @ core.js:4574 
onHandleError @ core.js:4648 
t.handleError @ polyfills.js:3 
r.runGuarded @ polyfills.js:3 
(anonymous) @ polyfills.js:3 
n.microtaskDrainDone @ polyfills.js:3 
o @ polyfills.js:3 
e.invokeTask @ polyfills.js:3 
p @ polyfills.js:2 
v @ polyfills.js:2 
IndexedDB (async) 
(anonymous) @ localforage.js:826 
t.invoke @ polyfills.js:3 
onInvoke @ core.js:4626 
t.invoke @ polyfills.js:3 
r.run @ polyfills.js:3 
(anonymous) @ polyfills.js:3 
t.invokeTask @ polyfills.js:3 
onInvokeTask @ core.js:4617 
t.invokeTask @ polyfills.js:3 
r.runTask @ polyfills.js:3 
o @ polyfills.js:3 
e.invokeTask @ polyfills.js:3 
p @ polyfills.js:2 
v @ polyfills.js:2

來源

2017-11-17 Sampath

getMyTopics方法不會返回任何內容。當catch運算符返回一個Observable時，它將返回一個空數組。

來源

2017-11-18 04:24:48 Christian

錯誤：未捕獲（承諾中）：TypeError：無法讀取未定義的屬性「映射」

回答

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