Book assignment question

I borrowed a book that has the following assignment:

Create a script with a function isPalindrome(x) which returns true if and only if x is a string that is a palindrome, that is, it reads the same forward an backwards: A man, a plan, a canal, Panama!

Can somebody help me with this?

 

One way:

function isPalindrome(strX) {
	var arrX = strX.split("");  //creates an array of the characters within strX
	arrX.reverse(); //reverse the array
	var Xrts = arrX.join("");  //join it back together, creating the reverse of strX
	return(strX == Xrts);  //return true if they match, false if they don't
}

Code (markup):

 

Or to improve on this we need to remove all punctuation and spaces using regex, and convert to lower-case:

function isPalindrome(strX) {
	strX = strX.replace(/[^a-zA-Z0-9]+/g,"").toLowerCase();  //leave only alphanumeric chararacters, and convert to lower case.
	return(strX == strX.split("").reverse().join(""));  //same as before but made into one line.
}
alert(isPalindrome("A man, a plan, a canal, Panama! "));

Code (markup):

 

strX.split("").reverse().join("") << this line may seem to strange to you but you can do this...

strX <<is a string object
.split("") <<is a function of a string, that splits the the string into an array...
.reverse() <<is a function of an array (which we now have because we split the string)
.join() <<.join() is basically the opposite of .split(), it joins the array back into a string..

So we have gone from string, to array, and back to string all in one line..