Letters Combinations

//02. Letters Combinations
function lettersCombinations(arg) {

  let char1 = arg.shift()
  let char2 = arg.shift()
  let char3 = arg.shift()

  let code1 = char1.charCodeAt(0)
  let code2 = char2.charCodeAt(0)
  let code3 = char3.charCodeAt(0)

  let output = ''
  let counter = 0
  for (i = code1; i <= code2; i++)
    for (j = code1; j <= code2; j++)
      for (k = code1; k <= code2; k++)
        if (i != code3 && j != code3 && k != code3) {
          counter++
          output += `${String.fromCharCode(i)}${String.fromCharCode(j)}${String.fromCharCode(k)} `
        }
  console.log(`${output}${counter}`)
}
lettersCombinations([
  'a',
  'c',
  'b'
])