We recently got the error
Can't resolve 'rxjs/add/operator/map' after upgrading Angular v5 to v6 and after a bit googled, we have found rxjs migration that guides us to install both
rxjs-compat at ^6.0.0.
Here is the command to install the rxjs packages for fixing the error:
npm install rxjs@6 rxjs-compat@6 --save
After you install the above two packages, the error should go away.
Learn more about rxjs migration guide.