type guard basique

Bonjour, c'est surement une question basique... pourquoi mon isUser() fonctionne mais pas mon isAdmin() ?

Code:

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interface User { name:string; age:number; } interface Admin extends User { isAdmin:boolean; } type UnknownUser = User|Admin;   function isUser(user:UnknownUser):user is User { return user.name === 'test'; } function isAdmin(user:UnknownUser):user is Admin { return user.isAdmin === true; }

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Property 'isAdmin' does not exist on type 'UnknownUser'.
Property 'isAdmin' does not exist on type 'User'.

j'ai l'impression que type UnknownUser = User|Admin; ne fait pas ce que je pense qu'il fait...

auto reponse : (apres plusieurs mois)

Code:

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function isAdmin(user: UnknownUser): user is Admin { return "isAdmin" in user && user.isAdmin === true; }

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