How to get the nth value of a JavaScript generator?

How can I get the nth value of a generator?

function *index() {
  let x = 0;
  while(true)
    yield x++;
}

// the 1st value
let a = index();
console.log(a.next().value); // 0

// the 3rd value
let b = index();
b.next();
b.next();
console.log(b.next().value); // 2

// the nth value?
let c = index();
let n = 10;
console.log(...); // 9

I wanted to avoid unnecessary creation of arrays or other intermediate values. Here's what my implementation of nth ended up like -

function nth (iter, n)
{ for (const v of iter)
    if (--n < 0)
      return v
}

Following the examples in the original question -

// the 1st value
console.log(nth(index(), 0))

// the 3rd value
console.log(nth(index(), 2))

// the 10th value
console.log(nth(index(), 9))

0
2
9

For finite generators, if the index is out of bounds the result will be undefined -

function* foo ()
{ yield 1
  yield 2
  yield 3
}

console.log(nth(foo(), 99))

undefined

Expand the snippet below to verify the results in your browser -

function *index ()
{ let x = 0
  while (true)
    yield x++
}

function* foo ()
{ yield 1
  yield 2
  yield 3
}

function nth (iter, n) {
  for (const v of iter)
    if (--n < 0)
      return v
}

// the 1st value
console.log(nth(index(), 0))

// the 3rd value
console.log(nth(index(), 2))

// the 10th value?
console.log(nth(index(), 9))

// out-of-bounds?
console.log(nth(foo(), 99))