Missing Letters using Regular Expressions?

Tell us what’s happening:
My code worked and passed, so I don’t have a problem with that but I was wondering if it would be possible to solve this using regular expressions. eg something like
toMatch = /[^a-z]/

Just curious?

Your code so far

function fearNotLetter(str) {
for (var i=0; i<str.length; i++){
var code=str.charCodeAt(i);
if(code!==str.charCodeAt(0) + i){
  return String.fromCharCode(code-1);

return undefined;


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Challenge: Missing letters

Link to the challenge:

I think we might need more of an explanation than just toMatch = /[^a-z]/ in order to answer your question. Would you give us more details about how you were thinking this could be solved?

I see no regular expression in your code?
Why not try it and if it fails add it to this post :3

Upon further discussion with my husband though of why you couldn’t use tomatch all the letters matching from a-z as if you weren’t given all the code from a-z it would likely return all the missing letters. Will investigate further as only new to this and if I can solve it in a different way might reply again.