Cookie are one way to store data in the browser.
document.cookie is a property of the browser document that returns the HTTP cookies that apply to the Document. If there are no cookies or cookies can't be applied to this resource, the empty string will be returned.
With the Web API and Document cookie property
You can browse the cookies with the devtool
or an browser extension. Example: Chrome extension Edit this cookie
Set two cookies
document.cookie = "name=nico"; document.cookie = "favorite_color=blue";
- Read the cookies. The cookies are in a string separated with a ;
console.log("All the cookies:"); console.log(document.cookie);
For the value of the google analytics cookie, see Google Analytics - Utma Cookie
- Only the cookie that starts with an underscore
console.log("All the cookies:"); console.log(document.cookie.split(";").filter( (item) => item.trim().startsWith('_') ));
We need to parse the value of document.cookie. This is a string of all cookies in a key pair format separated by a ;
- Setting a cookie
cookie_key = "name"; document.cookie = cookie_key+"=nico";
- Regular expression method. Because the key value is saved in variable, we cannot create a regular expression pattern as a string and need to use a regexp constructor
regexp = new RegExp("(?:(?:^|.*;\\s*)"+cookie_key+"\\s*\\=\\s*([^;]*).*$)|^.*$"); var cookieValue = document.cookie.replace(regexp, "$1"); console.log("Regular expression : The value of the cookie with the name key is ("+cookieValue+")");
- Functional Programming method
var cookieValue = document.cookie .split(";") .filter( (item) => item.trim().startsWith(cookie_key) ) .split("="); console.log("Functional Programming: The value of the cookie with the name key is ("+cookieValue+")");
To delete a cookie, just set the expiration date in the past.
document.cookie = "key=; expires=Thu, 01 Jan 1970 00:00:00 GMT";
- cookie can be send to a third party maliciously via Web Security - Cross-site request forgery (CSRF)