Add isPalindrome function to check for palindromes

Author: jyoung2419

leetcode3/정진영/125. Valid Palindrome

@@ -0,0 +1,15 @@
+/**
+ * @param {string} s
+ * @return {boolean}
+ */
+var isPalindrome = function(s) {
+    s = s.toLowerCase().replace(/[^a-z0-9]/g, "");
+
+    let m = "";
+
+    for (let i = s.length -1; i >= 0; i--){
+        m += s[i];
+    }
+
+    return s == m;
+};