Issue in auth.service.ts

registerUser(user) {
return this.http.post(this.domain + 'authentication/register', user).map(res => res.json());
}
// and others

i got some error in .map(res => res.json());

ERROR in src/app/services/auth.service.ts:22:74 - error TS2339: Property 'map' does not exist on type 'Observable'.

22 return this.http.post(this.domain +'/authentication/register',user ).map(res => res.json());

(https://user-images.githubusercontent.com/43374749/80504269-7bed9b80-89a5-11ea-8bd5-1e84d514b25b.png

https://user-images.githubusercontent.com/43374749/80504446-b6573880-89a5-11ea-8789-a9eb624e338b.png

core.js:6210 ERROR DOMException: Failed to execute 'open' on 'XMLHttpRequest': Invalid URL
at http://localhost:4200/polyfills.js:2873:35
at XMLHttpRequest.proto. [as open] (http://localhost:4200/polyfills.js:1462:52)
at Observable._subscribe (http://localhost:4200/vendor.js:60630:18)
at Observable._trySubscribe (http://localhost:4200/vendor.js:76149:25)
at Observable.subscribe (http://localhost:4200/vendor.js:76135:22)
at MapOperator.call (http://localhost:4200/vendor.js:81175:23)
at Observable.subscribe (http://localhost:4200/vendor.js:76130:31)
at RegisterComponent.onRegisterSubmit (http://localhost:4200/main.js:865:45)
at RegisterComponent_Template_form_submit_5_listener (http://localhost:4200/main.js:927:150)
at executeListenerWithErrorHandling (http://localhost:4200/vendor.js:26977:16)