Browser - Cookie

1 - About

HTTP cookies management in the client side (browser) via javascript.

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

3 - Management

3.1 - DevTool

You can browse the cookies with the devtool

or an browser extension. Example: Chrome extension Edit this cookie

3.2 - HttpOnly

A cookie set with the HttpOnly flag, tells the browser that Javascript cannot access this cookie (ie the cookie should only be managed by the server and set in the browser request)

3.3 - Set

Set two cookies

document.cookie = "name=nico";
document.cookie = "favorite_color=blue";

3.4 - Get

3.4.1 - All

  • Read the cookies. The cookies are in a string separated with a ;

console.log("All the cookies:");

For the value of the google analytics cookie, see Google Analytics - Utma Cookie

3.4.2 - Filter

  • Only the cookie that start with a underscore

console.log("All the cookies:");
console.log(document.cookie.split(";").filter( (item) => item.trim().startsWith('_') ));

3.4.3 - by name

There is no function in the Javascript Web API to get a cookie by name.

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. <note info>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</note>

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+")");

var cookieValue = document.cookie
    .filter( (item) => item.trim().startsWith(cookie_key) )[0]
console.log("Functional Programming: The value of the cookie with the name key is ("+cookieValue+")");

  • Result

3.5 - Delete

To delete a cookie, just set the expiration date in the past.

document.cookie = "key=; expires=Thu, 01 Jan 1970 00:00:00 GMT";

4 - Security Consideration

5 - Library

Data Science
Data Analysis
Data Science
Linear Algebra Mathematics

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