A cookie is often used to identify a user.
Examples of cookies:
In this example we will create a cookie that stores the name of a visitor. The first time a visitor arrives to the web page, he or she will be asked to fill in her/his name. The name is then stored in a cookie. The next time the visitor arrives at the same page, he or she will get welcome message.
First, we create a function that stores the name of the visitor in a cookie variable:
The parameters of the function above hold the name of the cookie, the value of the cookie, and the number of days until the cookie expires.
In the function above we first convert the number of days to a valid date, then we add the number of days until the cookie should expire. After that we store the cookie name, cookie value and the expiration date in the document.cookie object.
Then, we create another function that returns the value of a specified cookie:
The code above uses the indexOf() method to search for a cookie name inside the document's cookie string.
The first indexOf() method will return the position where the cookie is found. The " " + and +"=" is added so that the method don't find names or values containing the name.
If the method returns -1, the cookie may still exist at the very beginning of the cookie string. To eliminate this, another search is added, this time without the " " +.
Last, we create the function that displays a welcome message if the cookie is set, and if the cookie is not set it will display a prompt box, asking for the name of the user, and stores the username cookie for 365 days, by calling the setCookie function:
All together now:
The example above runs the checkCookie() function when the page loads.
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