Project Euler 004–JavaScript

25 02 2011

Problem 4

A palindromic number reads the same both ways. The largest palindrome made from the product of two 2-digit numbers is 9009 = 91 × 99.

Find the largest palindrome made from the product of two 3-digit numbers.


<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" ""&gt;

<html xmlns=""&gt;



    <title>Project Euler 004</title>


<body >

    <script type="text/javascript">


        function IsPalindrome(number)


            numberStr = number.toString();

            // simple palindrome test

            // we only have to go through the first

            // half of the letters

            for (c = 0; c < numberStr.length-c; c++)


                if (numberStr[c] !=

                    numberStr[numberStr.length-c-1]) {

                    return false;



            return true;



        answer = 0

        //here’s a familiar loop

        for(i = 100; i < 1000; i++)


            for(j = i; j < 1000; j++)


                product = i*j;

                if ((product > answer)

                && IsPalindrome(product))

                { answer = product; }




        document.write("<b>" + answer + "</b>");







Nothing too special here, but this is the one solution that didn’t use some sort of built in “reverse” function.  Still works.  Smile

If you have questions, leave a comment or please find me on Twitter (@azzlsoft) or email (



2 responses

9 06 2011
Talbot benoit

for (c = 0; c < numberStr.length – c; c++)

is not valid.. error

9 06 2011

Talbot, thanks for finding that. Try retyping the line in question. It appears as though the “-” (hyphen/minus) has been turned into a “–” (en dash) by Windows Live Writer. It’s a very subtle difference.

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