How can I set, get and destroy cookies in WordPress?

To set the cookie on wordpress I used the $domain value. With it I get to use the cookie value across the entire site.

$domain = ($_SERVER['HTTP_HOST'] != 'localhost') ? $_SERVER['HTTP_HOST'] : false;

setcookie("cookie_name", 'cookie_value', 0, '/', $domain);

To unset

setcookie("cookie_name", '', time()-1000, '/');

Try this code inside function.php to play with Cookies in WordPress

Set a Cookie in WordPress

add_action( 'init', 'my_setcookie' );
function my_setcookie() {
setcookie( 'my-name', 'my-value', time() + 3600, COOKIEPATH, COOKIE_DOMAIN   );
}

Get a Cookie in WordPress

add_action( 'wp_head', 'my_getcookie' );
function my_getcookie() {
$alert = isset( $_COOKIE['my-name'] ) ? $_COOKIE['my-name'] : 'not set';
 echo "<script type='text/javascript'>alert('$alert')</script>";
}

Delete or Unset a Cookie in WordPress

add_action( 'init', 'my_deletecookie' );
function my_deletecookie() {
setcookie( 'my-name', '', time() - 3600, COOKIEPATH, COOKIE_DOMAIN );
}

You can either retrieve and manipulate cookies on the server side using PHP or client side, using JavaScript.

In PHP, you set cookies using setcookie(). Note that this must be done before any output is sent to the browser which can be quite the challenge in Wordpress. You're pretty much limited to some of the early running hooks which you can set via a plugin or theme file (functions.php for example), eg

add_action('init', function() {
    if (!isset($_COOKIE['my_cookie'])) {
        setcookie('my_cookie', 'some default value', strtotime('+1 day'));
    }
});

Retrieving cookies in PHP is much easier. Simply get them by name from the $_COOKIE super global, eg

$cookieValue = $_COOKIE['my_cookie'];

Unsetting a cookie requires setting one with an expiration date in the past, something like

setcookie('my_cookie', null, strtotime('-1 day'));

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For JavaScript, I'd recommend having a look at one of the jQuery cookie plugins (seeing as jQuery is already part of Wordpress). Try http://plugins.jquery.com/project/Cookie