createSalaryObject.js

// A function that can take amount and currency as arguments
// and returns a salary object.
function createSalaryObject(amount, currency = "USD") {
  amount = Number(amount);
  currency = String(currency).trim().toUpperCase();
  currency = /^[A-Z]{3}$/.test(currency) ? currency : "USD";

  return {
    amount,
    currency,
    valueOf() { return amount },
    toString() { return `${currency} ${amount}` }
  };
}

// Create a new salary object
const salary = createSalaryObject(150000);

// Cast the salary object to a string (using String())
console.log(String(salary)); // "USD 150000"

// Cast the salary object to a string (using concatenation)
console.log("" + salary); // "150000"