Missing letters

[Lan1]

Please could someone explain how this solution works? I am stuck on if(charCode !== str.charCodeAt(0) + i)

This is from https://www.freecodecamp.org/learn/javascript-algorithms-and-data-structures/intermediate-algorithm-scripting/missing-letters

function fearNotLetter(str) {
 //using loop
 for(let i = 0; i < str.length; i++){
   const charCode = str.charCodeAt(i);
   //codes are：97-a 98-b 99-c 101-e
  
  if(charCode !== str.charCodeAt(0) + i){
   //why is charCode not starting from 97, and i being 3??
    return String.fromCharCode(charCode - 1)
  }
 }
return undefined;

}

console.log(fearNotLetter("abce"));

Thanks in advance!

[camperextraordinaire]

@Lan1

if(charCode !== str.charCodeAt(0) + i){

This checks if charCode is not equal to the character code str’s first character plus the current value of i. If the first letter in the string was a (charCode of 97), then the first iteration of the for loop, i would be 0, so the char code of the first letter would be the same as the In the case of str.charCodeAt(0) + i. During the second iteration, charCode would be b (charCode of 98) and since i would be 1, str.charCodeAt(0) + 1 would be the same charCode (98). This would keep going until the 4th iteration, where the charCode for e would be 101 and i would be 3. str.charCodeAt(0) + 3 would be 97 + 3 (or 100), so they would not match, and hence the return statement would return the letter before e.

[Lan1]

Ahhh so it keeps looping until the condition - if(charCode !== str.charCodeAt(0) + i) is met. Thank you for the explanation.