Non-null assertion operator !.

As of Typescript 2.0, you can enforce strict null checking with the --strictNullChecks flag.

Type checker throws an error if it can't determine whether a variable will be null or undefined at runtime. You may know that can't happen but the type checker doesn't know. You tell the type checker that it can't happen by applying the post-fix non-null assertion operator (!).

For example, after you use *ngIf to check that hero is defined, you can assert that hero properties are also defined:

<div *ngIf="hero">
  The hero's name is {{hero!.name}}
</div>

Unlike the safe navigation operator, the non-null assertion operator does not guard against null or undefined.