Hey Joshua, thank you for the comment and I'm happy you like the article. To quickly answer your question, of course don't 'need' to do it with partials but they are great advantages in using that approach. Let me try to give you a quick example as a basic use case.

Let's say we have a multiplier function that takes two arguments and returns the product. We will use that as our base

function multiply(x, y) {
  return x * y;
}

Now let's say we have the need to calculate often halves, doubles and triples. Partial function application will allow us to create generic, reusable, predictable and intuitive secondary functions as you can see below

const halves = multiply.bind(null, 0.5);
halves(2); // will output 1

const doubles = multiply.bind(null, 2);
doubles(5);  // will output 10

const triples = multiply.bind(null, 3);
triples(27); // will output 81

You get the idea. I will take a closer look at your solution here and give you some feedback on it. But in an interview context it might be best to solve against the specs first then propose a better alternative.

Let me know what you think.

Cheers

Thanks for your response.

The computation of gross can be a partial application since it can be reused, this also helps for readability.

Thanks in advance for your feedback.