match a longprefix

longPrefix.js

function longPrefix(arr) {
  let result = ''
  if (arr.length === 0) return result
  for (let i = 0; i < arr[0].length || 0; i++) {
    for (let j = 1; j < arr.length; j++) {
      if (arr[0][i] === arr[j][i]) {
        if (j + 1 === arr.length) {
          result += arr[0][i]
        }
      } else {
        return result
      }
    }
  }
  return result
}
console.log(longPrefix(['outside', 'outdated'])) // out