finding the logic error in a greetUser function

My professor says I have a logic error in the greetUser function of code I was already graded on. The code is based on the example in the text, so I'm stunned as to determining the logic. This was her message to me:

The greetUser function is not reading the cookie correctly for the returning visitor. Check this line of code in the readCookie function - it has a logic error.

This is the readCookie function:

function readCookie(name) {
    开发者_如何学运维var nameEQ = name + "=";
    var x = document.cookie.split(';');
    for(var i=0;i < ca.length;i++) {
        var c = cookies[i];
        while (c.charAt(0)==' ') c = c.substring(1,c.length);
        if (c.indexOf(nameEQ) == 0) return c.substring(nameEQ.length,c.length);
    }
    return null;
}

This is the greetUser function:

function greetUser(){
    userName = readCookie("rock_username");
    if(userName)
        alert("Hello " + userName + ", I missed you.");
    else 
        alert("Hello, I am your pet rock");
}

From my novice eyes it all looks logical to me, the same as it was in the text example. Any suggestions

var x = document.cookie.split(';');
for(var i=0;i < ca.length;i++) {
var c = cookies[i];

You are iterating on "ca" (what is that?) instead of "x", and then you are reading from the cookies array? 3 different variables, same meaning?

I'll explain: var x = document.cookie.split(';'); splits the string stored in document.cookie into an array, that will effectively be held inside the x parameter.

Then, inside the for() construct, you are increasing i up until the amount of elements found inside the array you just created from splitting the string. That way, each time you do c = x[i]; (correct version) you will get the next portion of the document.cookie string that you split with the ';' character.

This allows you to work on all the interesting parts of document.cookie, which are, by definition, the user agent (browser) cookies. In your example, you are iterating over the cookies to find a specific one - the 'name' cookie - in order to print it as a greet to the user.

Good luck!