Function in the another function: isPalindrome is not a function

Question

I'm trying to write a function that takes another function and then executes it in reverse. And it don't work :( Mistake is: TypeError: isPalindrome is not a function. Where is a problem?

const isPalindrome = (text) => {
  let text1 = text.toLowerCase();
  let text2 = text1.split('').reverse().join('');
  return text1 === text2;
}

const isNotPalindrome = (isPalindrome) => {
  !isPalindrome();
};

You are changing the content of `isPalindrome` inside the scope of the function. Rename the argument. — Christopher, Jun 03 '22 at 17:43
You are seeing a case of variable shadowing: https://stackoverflow.com/q/53734399/4088472 — Slava Knyazev, Jun 03 '22 at 17:44
_"executes it in reverse"_: what does that mean? `isPalindrome` already returns a boolean. Why not simply log that result instead? `isNotPalindrome` seems unnecessary. — Andy, Jun 03 '22 at 17:47

score 0 · Answer 1 · answered Jun 03 '22 at 21:35

If you really want to encapsulate it into a method you can do that:

const isPalindrome = (text) => {
  let text1 = text.toLowerCase();
  let text2 = text1.split('').reverse().join('');
  return text1 === text2;
}

const isNotPalindrome = (text) => !isPalindrome(text);

console.log(isPalindrome('test'));
console.log(isNotPalindrome('test'));

However, since it does not make really sense to create a method to just return the opposite you could simply do:

const isPalindrome = (text) => {
  let text1 = text.toLowerCase();
  let text2 = text1.split('').reverse().join('');
  return text1 === text2;
}

console.log(isPalindrome('test'));
console.log(!isPalindrome('test'));

Function in the another function: isPalindrome is not a function

1 Answers1