Assignment: map/filter/reduce refresher

Implement a function named palindrome that tells whether a given string is the same when read left-to-right and right-to-left, ignoring upper/lowercase differences and any characters outside a to z. For example:

palindrome('ABBA')                              // true
palindrome('Abba')                              // true
palindrome('A man, a plan, a canal: Panama!')   // true

You must use the following helper functions (they are provided):

const str2chars = str  => [...str];            // convert a string to an array of chars
const isAlpha   = char => char.match(/[a-z]/); // char is in the alphabet

💡

The question title contains implementation hints.

Solution

const palindrome = str => {
  const alphaChars = str2chars(str).map(char => char.toLowerCase()).filter(isAlpha);
  return alphaChars.join('') === alphaChars.reverse().join('');
};

Your solution will be tested against:

palindrome("Amore, Roma!")
&& palindrome("Madam, I'm Adam!")
&& palindrome("Never odd or even.")
&& !palindrome("Amore")

Quiz 24a Quiz28m