Substring fun

/*
Description:
Function nthChar takes 1 parameter - an array of words.

You must concatenate the nth letter from each word to construct a new word which should be returned as a string.

Note: Test cases contain valid input only - i.e. a string array or an empty array, each word will have at least as many letters as its ordinal position.
*/
function nthChar(words){
  let str='';
  for (let i=0;i<words.length;i++){
  str+=words[i][i]
  }
 return words.length?str:''
}