How can we transform the `toUSD(amount)` function into a prototype function?

This function is functioning perfectly as intended.

function toUSD(amount): string {
  // CONVERT number to $0.00 format
  return new Intl.NumberFormat("en-US", {
    style: "currency",
    currency: "USD"
  }).format(amount);
};

Here is how I currently implement it:

console.log(toUSD(123)); // result = $123.00

What modifications should be made to use it like this?

console.log((123).toUSD()); // output = $123.00

Answer №1

Your function must reference the current number without using input parameters. Instead, use this to access the value:

function toUSD(this: number): string {
  return new Intl.NumberFormat("en-US", {
    style: "currency",
    currency: "USD"
  }).format(this);
};

Next, you can add it to Number.prototype as suggested by Ximaz's answer:

Number.prototype.toUSD = toUSD;

Now you can call it like (123).toUSD() and get the output of $123.00.

Answer №2

In order to correctly utilize the prototype feature, it should be implemented as follows:

function toUSD(this: number) { ... }     // Define the function

Number.prototype.toUSD = toUSD // Assign the function to Number's prototype

console.log((123).toUSD());    // Expected output: $123.00

Upon reviewing the solution, I realized my mistake was not understanding the importance of the this keyword. Lesson learned!

Unfortunately, I'm getting a $NaN output on my local machine, but the display indicates that the prototype assignment was successful.

(Based on the correct solution, this may be due to missing the use of the this keyword)

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