Type 'string' is not assignable to type 'keyof code example

Example 1: Type 'string | undefined' is not assignable to type 'string'.

let name1:string = person.name as string;

Example 2: Type 'string | undefined' is not assignable to type 'string'.

let name1:string = person.name!; 
//                            ^ note the exclamation mark here