createSalaryObject_modified.js

function createSalaryObject(amount, currency = "USD") {
  amount = Number(amount);
  currency = String(currency).trim().toUpperCase();
  currency = /^[A-Z]{3}$/.test(currency) ? currency : "USD";

  // The string equivalent for amount (with currency)
  const amountString = `${currency} ${amount}`;

  return {
    amount,
    currency,
    valueOf() { return amount },

    // Return `amountString` from `toString()`
    toString() { return amountString },

    // Define a `[Symbol.toPrimitive]` method.
    // Returns `amountString` for "default" hint.
    [Symbol.toPrimitive](hint) {
      return hint === "number" ? amount : amountString;
    }
  };
}

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

// Both String() function and string concatenation
// now yield the same result.
console.log(String(salary)); // "USD 150000"
console.log("" + salary);    // "USD 150000"