longestCommonPrefix.js

function longestCommonPrefix ( arr ) {
  var result = "";
  var firstWord = arr[0];

  for ( var i = 0; i < firstWord.length; i++ ) {
    for ( var j = 0; j < arr.length; j++) {
      if ( firstWord[i] === arr[j][i]) {
         continue;
      } else {
         return result;
      }
    }
    result += firstWord[i];
  }
}

// longestCommonPrefix(['hello', 'hellos', 'helium', 'help']) => 'hel'