Give me a Diamond.js

// Jamie is a programmer, and James' girlfriend. She likes diamonds, and wants a diamond string from James. Since James doesn't know how to make this happen, he needs your help.

// Task
// You need to return a string that looks like a diamond shape when printed on the screen, using asterisk (*) characters. Trailing spaces should be removed, and every line must be terminated with a newline character (\n).

// Return null/nil/None/... if the input is an even number or negative, as it is not possible to print a diamond of even or negative size.

// Examples
// A size 3 diamond:

//  *
// ***
//  *
// ...which would appear as a string of " *\n***\n *\n"

// A size 5 diamond:

//   *
//  ***
// *****
//  ***
//   *
// ...that is:

// "  *\n ***\n*****\n ***\n  *\n"


function diamond(n){
   if ((n % 2 === 0) || (n < 0)) {
    return null
  } else {
    let diamondLine = ""
    for (let i = 1; i <= n; i += 2){
      let whitespace = " ".repeat((n - i) / 2);
      let stars = "*".repeat(i);
      let line = whitespace + stars  + "\n"
       diamondLine += line;
    }
    for (let i = n - 2; i > 0; i -= 2){
      let whitespace = " ".repeat((n - i) / 2);
      let stars = "*".repeat(i);
      let line = whitespace + stars + "\n"
       diamondLine += line;
    }
    return diamondLine
  }
  
}


// top solution on codewars

function diamond (n) {
  if (n <= 0 || n % 2 === 0) return null
  str = ''
  for (let i = 0; i < n; i++) { 
    let len = Math.abs((n-2*i-1)/2)
    str += ' '.repeat(len)
    str += '*'.repeat(n-2*len)
    str += '\n'
  }
  return str
}