Javascript: How do I use the same function with different parameters?

Question

I would be forever grateful if you could enlighten me how to get it to work. Currently when I run it it gives the alert upon the first entered username.

let userName1;
let userName2;
let userName3;

alcoholAgeCheck();
alcoholAgeCheck(userName2);
alcoholAgeCheck(userName3);

function alcoholAgeCheck() {
  userName1 = prompt('Enter name');

  if (userName1 === userName2 || userName1 === userName3) {
    alert('Sorry, you may only use the same name once');
  } else if (userName2 === userName1 || userName2 === userName3) {
    alert('Sorry, you may only use the same name once');
  }
}

If you don't give a value to userName2 and userName3, than userName2 === userName3 will always be valid. — Gerard
– Gerard, Commented Oct 4, 2021 at 22:52
@Gerard What value do I give them? I just want to find a way to have it run once with userName1, once with userName2 and once with userName3 — helpme
– helpme, Commented Oct 4, 2021 at 22:54
Taking your question at face value, the code you're looking for is: jsfiddle.net/1p3q8axw However that is a bad approach for multiple reasons and you shouldn't use it at all. — user5734311
– user5734311, Commented Oct 4, 2021 at 23:24

Barmar · Accepted Answer · 2021-10-04 22:57:31Z

3

Save all the previous inputs in a variable, and check whether the new input is in the set.

const userNames = new Set();

function alcoholAgeCheck() {
  userName = prompt('Enter name');
  if (userNames.has(userName)) {
    alert('Sorry, you may only use the same name once');
  } else {
    userNames.add(userName);
  }
}

alcoholAgeCheck();
alcoholAgeCheck();
alcoholAgeCheck();
console.log(Array.from(userNames));

edited Oct 4, 2021 at 22:57

answered Oct 4, 2021 at 22:49

Barmar

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5 Comments

Zak Over a year ago

The only thing I would add to this is a console.log() afterward so the OP can see what you did here. Great solution.

helpme Over a year ago

@Barmar Hi Barmar, thank you for this solution. I've yet learned new Set and Has. Is there a way for me to write it with my code, with just giving values to the variables?

user5734311 Over a year ago

@helpme No, because that's not how function parameters work in JS. What you're trying to do is called "pass by reference" and possible in for instance C, but not in JS. In JS, it's always "pass by value".

connexo Over a year ago

Why would one pick a Set over a simple Array here?

Barmar Over a year ago

@connexo Searching a set is more efficient. But for small quantities, an array and .includes() would be fine.

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