Understanding JavaScript Cookies: A Comprehensive Guide with Example Code


If you’ve ever used a website that remembers your preferences or login information, you’ve likely interacted with cookies. Cookies are small text files that are stored on a user’s computer by a website. They allow websites to remember a user’s actions and preferences, making for a more personalized experience.

JavaScript is a popular programming language for creating interactive websites, and it has built-in functionality for working with cookies. In this article, we’ll explore how cookies work in JavaScript and provide example code to help you get started.

How Cookies Work:

When a user visits a website that uses cookies, the website sends a small text file to the user’s computer, which is stored in their web browser. This file contains information about the user’s activity on the website, such as login credentials or preferences. The next time the user visits the website, the browser sends the cookie back to the website, allowing it to retrieve the stored information.

Cookies can be set to expire after a certain amount of time, or they can be stored indefinitely. They can also be set to be accessible only by the website that created them, or they can be made accessible by other websites as well.

Why Cookies are Useful:

Cookies have many practical uses for websites. For example, they can be used to remember a user’s login information, saving them the trouble of having to enter their credentials every time they visit the site. Cookies can also be used to personalize a website’s content, displaying relevant information based on a user’s preferences or past activity.

Cookies can also be used to track user behavior, which can be useful for analytics and marketing purposes. However, it’s important to note that cookies can also raise privacy concerns, as they can be used to collect and store sensitive information about users.

Using Cookies in JavaScript:

JavaScript has built-in functionality for working with cookies. The document.cookie property allows you to read and write cookies, while the Date object can be used to set cookie expiration dates.

To set a cookie in JavaScript, you can use the following syntax:

document.cookie = "cookieName=cookieValue";

To set a cookie with an expiration date, you can use the following syntax:

var expirationDate = new Date();
expirationDate.setMonth(expirationDate.getMonth() + 1);
document.cookie = "cookieName=cookieValue;expires=" + expirationDate.toUTCString();

To read a cookie in JavaScript, you can use the following syntax:

var cookies = document.cookie.split(";");
for (var i = 0; i < cookies.length; i++) {
  var cookie = cookies[i].trim();
  if (cookie.startsWith("cookieName=")) {
    var cookieValue = cookie.substring("cookieName=".length, cookie.length);
    // do something with cookieValue


Cookies are a powerful tool for creating personalized and interactive websites, and JavaScript provides built-in functionality for working with them. By understanding how cookies work and how to use them effectively, you can create websites that provide a more engaging and user-friendly experience. With the example code provided in this article, you’ll be well on your way to mastering cookies in JavaScript.