Very often we have use-cases where we would like to use a single type Union Type but still be sure about the properties inside them. interface Employee { : string; salary: number; } interface HumanResource { : string; power: boolean; } person: Employee | HumanResource; name name let But under the hood Typescript union's are more of "common" properties inside them instead of "having all the properties". So when you try and use it like: helloPerson = (person: Employee | HumanResource): { .log(person.<only has properties common to Employee & HumanResource aka name>); } let => void console Whereas, you would expect person to have {name, salary} or {name, power} and choose between them depending on what person is. This is where discriminators come in power-play. Bear with my variable nomenclature: Let's define an enum to contain both the use-cases of Person's we have, calling it PersonType and then define a type combining `HumanResource` and `Employee` enum PersonType { , } interface Employee { : string; type: PersonType.EMPLOYEE salary: number; } interface HumanResource { : string; type: PersonType.HR power: boolean; } type Person = HumanResource | Employee; person: Employee | HumanResource; helloPerson = (person: Person): { (person.type) { PersonType.EMPLOYEE: .log(person.{gives you name, salary}); } } "EMPLOYEE" "HR" name name let let => void switch case // this gives you both name/salary since now TS understands // and discriminates between the two types you have console This way you can access properties of only a certain interface based on the type which avoids accessing non-belonging properties and using "as". Hope you learned something new and discriminators go a long way in helping you.
