radixSort.js

const digit = (num, pos) => {
  const str = num.toString()[pos]
  return typeof str === "undefined" ? 0 : parseInt(str)
}

const maxDigits = input => input.reduce((accum, value) => {
  const len = value.toString().length
  return accum < len ? len : accum
}, null)

const convertSorted = rad => rad.reduce((accum, value) => {
  if (Array.isArray(value)) {
    return accum.concat(value) 
  } else {
    return accum
  }
},[])

const ex = [999, 10, 53, 194]

function radixSort(input) {

  const numDigits = maxDigits(input)
  let current = 0
  
  let rad = []
  let sorted = input
  
  
  while (current <= numDigits) {
    rad = []
    
    for (let i = 0; i < sorted.length; i++) {
      const dig = digit(sorted[i], current)
      
      if (typeof rad[dig] === "undefined") {
        rad[dig] = []
      }
      
      rad[dig].push(sorted[i])
      
    }
    
    sorted = convertSorted(rad)
    current++
  }
  
  return sorted
}



console.log(radixSort(ex))