Angular Route Guard - Part 1 : canActivate guard using CanActivateFn

Angular CanActivateFn provides functional approach to write code for canActivate route guard.
To perform canActivate route guard, we need to know following points.
1. CanActivateFn : Signature of a function to perform canActivate route guard.
2. canActivate : A property of Route interface that accepts an array of CanActivateFn instances.
3. mapToCanActivate : Maps injectable classes containing a method named as canActivate to an array of equivalent CanActivateFn.