employeeInterface.ts

// Interface can also be called a contract.
// We can use them to define custom types without creating classes.
// Interfaces ARE NOT compiled to JavaScript! It's just for checking/validation done by our TypeScript compiler.

// Employee interface
interface Employee {
    employeeName: string;
    salary: number;
    mobileNumber?: string; // Optional property => Does not have to be implemented
}

let employee: Employee;

// This value does not satisfy the interface => Compilation error
// user = { anything: 'anything', anynumber: 5};

// This value does satisfy the interface
employee = {employeeName: 'John', salary: 1234};

console.log(employee);

// Result => { employeeName: 'John', salary: 1234 }