Getting NaN instead of numbers in javascript

Question

I am trying to get a range of numbers by converting alphabet to numbers and then comparing them with one another to see if they match or not. I can change my approach but I don't understand why is it happening.

function fearNotLetter(str) {
  let left=0
  let right=str.length-1
  for(let i in str) {

    let alphaNum=str.charCodeAt(i) //gives number
    let alphaNum2=str.charCodeAt(i+1) //gives 98 for the first and then NaN for the rest

    console.log(i, alphaNum, alphaNum2)
  }
  

}
fearNotLetter("abce")
fearNotLetter("abcdefghjklmno")

Answer 1

Convert string to integer, for-in loop gives string as key:

function fearNotLetter(str) {
  let left=0
  let right=str.length-1
  str.split().forEach((char, i) => {

    let alphaNum=str.charCodeAt(i) //gives number
    let alphaNum2=str.charCodeAt(i+1) //gives 98 for the first and then NaN for the rest


  });
  

}
// fearNotLetter("abce")
fearNotLetter("abcdefghjklmno")