captcha code is showing undefined in ie7?

Question

My captcha code is working fine in all browsers, but it is showing error in ie7.

Here is the fiddle : http://jsfiddle.net/KMupW/4/

Here is my code :

function randomString(length, chars) {
    var result = '';
    for (var i = length; i > 0; --i) result += chars[Math.round(Math.random() * (chars.length - 1))];
    return result;
}
 var code= randomString(5,'0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ');

 document.getElementById("txtCaptcha").value = code;
 document.getElementById("txtCaptchaDiv").innerHTML = code;  

Answer 1

result += chars[index];

Problem is here, internet explorer doesn't support string manipulation like arrays, you should write this instead:

result += chars.charAt(index);

So the line should finally be:

result += chars.charAt(Math.round(Math.random() * (chars.length - 1)));

An example: http://jsfiddle.net/XDxR7/2/