transposeTwoStrings.js

function transposeTwoStrings (string1, string2) {
  var i = 0
  
  // Continue checking each letter of each string as long as at least one of the strings still has letters
  while (string1[i] !== undefined || string2[i] !== undefined) {
    var letterColumn = '';
    
    // As long as the index we're at still has a letter, append it to the string, otherwise append an empty space
    if (string1[i] !== undefined) {
      letterColumn = letterColumn.concat(string1[i]);
    } else {
      letterColumn = letterColumn.concat(' ');
    }
    
    // Space between the two letter columns
    letterColumn = letterColumn.concat(' ');
    
    // Same as above with string1
    if (string2[i] !== undefined) {
      letterColumn = letterColumn.concat(string2[i]);
    } else {
      letterColumn = letterColumn.concat(' ');
    }
    
    // Increment the index
    i++;
    
    // Print each letter column to the console
    console.log(letterColumn);
  }
}