`slice(1, -1)`って何してるの - 回文の真偽判定を再帰的に解く - Qiita

function isPalindrome (str) { let len = 0; // remove non-alphanumeric characters and // change the string to lowercase // and get the length of the string str = str.replace(/[^a-z0-9]/i, '').toLowerCase(); len = str.length; // calculate the string midpoint position and // loop through the characters up to the midpoint // comparing characters in corresponding positions // from the start of the stri