Once you have extracted the value of a cookie from the cookie property, you must interpret that value based on whatever format or encoding was used by the cookie's creator. For example, the cookie might store multiple pieces of information in colon-separated fields. In this case, you would have to use appropriate string methods to extract the various fields of information. Don't forget to use the unescape( ) function on the cookie value if it was encoded using the escape( ) function.

The following code shows how you might read the cookie property, extract a single cookie from it, and use the value of that cookie:

// Read the cookie property. This returns all cookies for this document.
var allcookies = document.cookie;
// Look for the start of the cookie named "version"
var pos = allcookies.indexOf("version=");

// If we find a cookie by that name, extract and use its value
if (pos != -1) {
    var start = pos + 8;                       // Start of cookie value
    var end = allcookies.indexOf(";", start);  // End of cookie value
    if (end == -1) end = allcookies.length;
    var value = allcookies.substring(start, end);  // Extract the value
    value = unescape(value);                       // Decode it

    // Now that we have the cookie value, we can use it.
    // In this case, the cookie was previously set to the modification
    // date of the document, so we can use it to see if the document has
    // changed since the user last visited.
    if (value != document.lastModified)
        alert("This document has changed since you were last here");
}