Error: (40, 20) TS2339: 'map' property does not exist on type 'string | Book | Book[]'. 'Map' property does not exist on type 'string'

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I am implementing @ngrx in angular2 app and when try to compile the typescript project I am getting below error.

Error:(40, 20) TS2339:Property 'map' does not exist on type 'string | Book | Book[]'. Property 'map' does not exist on type 'string'.

I think the error is related to union type of typescript which is used in the ngrx example app

link to the app


It is really hard to tell without seeing your code and getting more details, but it looks like you are trying to do a map on the object returned by the Observable instead of mapping the actual Observable.