Change every letter in the string to the letter following it in the alphabet, so a becomes b, z becomes a, etc

Question

So i was trying to solve this challenge in coderbyte. 
I understand the given answer except for the following:
javascript
String.fromCharCode(char.charCodeAt() + 1);

Where does that String come from? Where does fromCharCode gets its values from?
How does it know it needs to take any value from the regExpression 
javascript
/[a-z]/gi

?
Here goes the whole code:
```javascript
function letterChanges(str) { 
  const converted = str.replace(/[a-z]/gi, function(char) { 
    return (char === 'z' || char === 'Z') ? 'a' : String.fromCharCode(char.charCodeAt() + 1);
  });
  const capitalized = converted.replace(/a|e|i|o|u/gi, function(vowel) { 
    return vowel.toUpperCase();
  });
  return capitalized;         
}
console.log (letterChanges("Anda a lavarte el ...alma"));   
```
Is there anybody out there that could please help me understand that piece of code? Thanks

Clayton Perszyk · Accepted Answer

String is a global JS object constructor and, like other global objects, it has methods (some also have properties). One method is fromCharCode, which takes a character code (ie a number that corresponds to a character), and returns the character for that code.
Concerning code, i'll add comments to clarify:
```js
function letterChanges(str) { 
// here str will call replace for any char that is a-z and will grab all, not just first (eg 'g' flag) and will avoid case (eg 'i' flag)
  const converted = str.replace(/[a-z]/gi, function(char) {  // the function will apply to each char
   // example: char = 'a' -> char.charCodeAt() -> returns 97 -> 97 + 1 = 98 -> String.fromCharCode(98) -> return 'b'  
    return (char === 'z' || char === 'Z') ? 'a' : String.fromCharCode(char.charCodeAt() + 1);
  });
  const capitalized = converted.replace(/a|e|i|o|u/gi, function(vowel) { 
    return vowel.toUpperCase();
  });
  return capitalized;         
}
console.log (letterChanges("Anda a lavarte el ...alma"));  
```

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RODRIGO MARTINEZ

RODRIGO MARTINEZ

Change every letter in the string to the letter following it in the alphabet, so a becomes b, z becomes a, etc

1 Answer

Clayton Perszyk

Clayton Perszyk

RODRIGO MARTINEZ

RODRIGO MARTINEZ