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HTML / CSS / JS

interface Employee {
    id: number;
    name: string;
    email: string;
    salary: number;
    department: string;
    startDate: Date;
}

// Pick — select only certain properties
type EmployeeCard  = Pick<Employee, "id" | "name" | "department">;
type PublicProfile = Pick<Employee, "name" | "email">;

// Omit — exclude certain properties
type EmployeeDTO    = Omit<Employee, "salary">;          // no salary
type NewEmployeeDTO = Omit<Employee, "id" | "startDate">; // no id/date yet

// ReturnType and Parameters
function createUser(name: string, email: string, age: number) {
    return { id: Math.random(), name, email, age, createdAt: new Date() };
}

type UserResult  = ReturnType<typeof createUser>;
// { id: number; name: string; email: string; age: number; createdAt: Date }

type CreateParams = Parameters<typeof createUser>;
// [name: string, email: string, age: number]

// InstanceType
class DatabaseConnection {
    constructor(public url: string) {}
    query(sql: string): unknown[] { return []; }
}

type DBInstance = InstanceType<typeof DatabaseConnection>;
// DatabaseConnection