Я изменяю некоторый код в isPalindrome и добавляю div для получения результата.
function isPalindrome (userEntry) {
var re = /[\W_]/g;
var lowRegStr = userEntry.toLowerCase().replace(re, '');
var reverseStr = lowRegStr.split('').reverse().join('');
if( reverseStr === lowRegStr){
document.getElementById("output").innerHTML = "Your word is a palindrome";
}
}
<h2>Palindrome detection</h2>
<code>Detect if a string is a palindrome</code><br /><br />
Enter a word with 10 or less characters <input type="text" id="userEntry"><br />
<button type="button" onclick="isPalindrome(document.getElementById('userEntry').value)">Enter</button><br /><br />
<div id="output"></div>