[typescript] Typescript: Type 'string | undefined' is not assignable to type 'string'

Solution 1: Remove the explicit type definition

Since getPerson already returns a Person with a name, we can use the inferred type.

function getPerson(){
  let person = {name:"John"};
  return person;
}

let person = getPerson();

If we were to define person: Person we would lose a piece of information. We know getPerson returns an object with a non-optional property called name, but describing it as Person would bring the optionality back.

Solution 2: Use a more precise definition

type Require<T, K extends keyof T> = T & {
  [P in K]-?: T[P]
};

function getPerson() {
  let person = {name:"John"};
  return person;
}

let person: Require<Person, 'name'> = getPerson();
let name1:string = person.name;

Solution 3: Redesign your interface

A shape in which all properties are optional is called a weak type and usually is an indicator of bad design. If we were to make name a required property, your problem goes away.

interface Person {
  name:string,
  age?:string,
  gender?:string,
  occupation?:string,
}