block3.ts

function hasAttributeName(a: object): a is { name: string } {
    return typeof ((a as any).name) === 'string';
}
const user: object = {name: 'Georges'};
console.log(user.name) // Compile error: Property 'name' does not exist on type 'object': 
if (hasAttributeName(user)) {
   console.log(user.name) // Compile fine. 
   // With the type guard, the compiler now knows that user is of type {name: string}
}