1) Animations:

Animations functions were part of @angular/core module. So this code always being there even though it has not been used. So now in Angular 4, animations are now provided in the module BrowserAnimationsModule which resides under @angular/platform-browser/animations.

2) *ngIf was provided for the conditional formatting in Angular 2. At that time, if any opposite condition needed then, we needed to write again *ngIf with that opposite condition. To remove this issue, Angular 4 has introduced else. This can be used for the else condition.

3) Forms get assigned "novalidate" automatically.

4) AOT compiled templates in Angular 4 are very small in size and which improves the loading speed of the page

5) Changed extend to implement. Classes are not allowed to implement events via inheritance. So instead of that, we need to use interface approach.

i.e. cname implements OnInit

6)