Why Can't I Use Variables In Loops?

JavaScript
#1

This code works:

function countAllCharacters(str) {

  var newObj = {}
  for (var i = 0; i < str.length; i++) {
      if ( newObj[str[i]] === undefined) {
          newObj[str[i]] = 1
      } else {
          newObj[str[i]] += 1
      }
  }
  return newObj
}

countAllCharacters('hi')

But this doesn’t:

function countAllCharacters(str) {

  var newObj = {}
  for (var i = 0; i < str.length; i++) {
      var currentLetter = newObj[str[i]]
      if ( currentLetter === undefined) {
          currentLetter = 1
      } else {
          currentLetter += 1
      }
  }
  return newObj
}

countAllCharacters('hi')

These are the same thing, aren’t they? I’ve encountered this problem several times.

#2

In the first case, you are modifying the contents of the newObj, but in the second you are not.

currentLetter is just a variable with the contents of newObj[str[i]], not a reference to newObj[str[i]].

1 Like
#3