Javascript setting and getting cookies

How to create and read cookies in JavaScript

An HTTP cookie (also known as web cookie, browser cookie) is a small piece of information stored by the server in the user’s browser. Cookies are commonly used for session management, user-tracking, and storing user preferences.

In JavaScript, you can use the document.cookie property to create, read, and delete cookies. Note that the document.cookie property can only access cookies with the HttpOnly attribute unspecified.

document.cookie = 'name=John Doe' 

Since the cookie value can not contain semicolons, commas, or spaces, you need the encodeURIComponent() function to encode the value before storing it in the cookie:

document.cookie = `name=$encodeURIComponent('John Doe')>` 

Note: When you set the value of document.cookie , the web browser does not overwrite existing cookies. Instead, it adds a new HTTP cookie to the user’s computer.

By default, the above cookie lifespan is the current browser session, which means that it is removed when the user closes the browser. Such cookies are called session cookies. To persist cookies beyond the current browser session, you need to specify its expiry date either using the expires attribute (in UTC/GMT format) or the max-age attribute (in seconds):

// Set cookie fixed expiration date document.cookie = `name=$encodeURIComponent('John Doe')>; expires=Sun, 14 August 2022 03:11:45 UTC` // Set cookie max age, e.g. expire after 7 days document.cookie = `name=$encodeURIComponent('John Doe')>; max-age=$7 * 24 * 60 * 60>` 

By default, a cookie is available to all web pages in the same directory and its subdirectories. However, you can explicitly specify a path attribute to ensure that the cookie is only accessible to that path and its subdirectories. For example, if set the path to / , the cookie will be available throughout the website regardless of which page creates it:

document.cookie = `name=$encodeURIComponent('John Doe')>; path=/` 

The cookies, by default, are available only to the web pages in the domain they were used to set in. However, you can use the domain attribute to make a cookie available across subdomains. For exmaple, if a cookie created by a web page on help.example.com sets its path to / and its domain to example.com , that cookie is also available to all web pages on blog.example.com , dash.example.com , etc.

document.cookie = `name=$encodeURIComponent('John Doe')>; path=/; domain=example.com` 

You can also make a cookie secure using the secure attribute. Such cookies are only transmitted over a secure (i.e. encrypted) connection such as HTTPS:

document.cookie = `name=$encodeURIComponent('John Doe')>; path=/; domain=example.com; secure` 

Finally, let us write a JavaScript function that takes in the name, value, expiry days, path, and domain, and adds an HTTP cookie:

const setCookie = (name, value, days, path, domain, secure) =>  let cookie = `$name>=$encodeURIComponent(value)>` // Add expiry date if (days)  const expiry = new Date() expiry.setDate(expiry.getDate() + days) cookie += `; expires=$expiry.toUTCString()>` > // Add Path, Domain, and Secure if (path) cookie += `; path=$path>` if (domain) cookie += `; domain=$domain>` if (secure) cookie += `; secure` // Set an HTTP cookie document.cookie = cookie > 

setCookie('name', 'John Doe', 90); 

The document.cookie property returns all cookies set by the server as a series of key-value pairs separated by semi-colons:

const cookies = document.cookie console.log(cookies) // _ga=GA1.2.315746813.1624003242; lesson_completed=false; theme=dark 

Since all the values and names are URL-encoded, you have to decode them using the decodeURIComponent() method. Let us write a function that takes the cookie name as input and returns its value. If the cookie is not found, it should return a null value.

const getCookie = name =>  const cookies = document.cookie.split(';') for (let i = 0; i  cookies.length; i++)  let c = cookies[i].trim().split('=') if (c[0] === name)  return decodeURIComponent(c[1]) > > return '' > console.log(getCookie('_ga')) // GA1.1.1736818142.1621579881 

The above code uses the JavaScript split() method to split the cookie string by semi-colon. Then it iterates through the result array to match the name of the requested cookie with the key-value pairs.

You can update a cookie in the same way as you create it with the same name, path, domain, and secure option:

document.cookie = 'name=Alex; expires=Mon, 15 August 2022 10:52:32 UTC' 

Deleting a cookie is very simple. All you need to do is set the expiration date to some time in the past with the same name, path, domain, and secure option:

document.cookie = "name=; expires=Thu, 01 Jan 1970 00:00:00 UTC" 

Read Next: How to use cookies in Spring Boot ✌️ Like this article? Follow me on Twitter and LinkedIn. You can also subscribe to RSS Feed.

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JavaScript Cookies

When a browser requests a web page from a server, cookies belonging to the page are added to the request. This way the server gets the necessary data to «remember» information about users.

None of the examples below will work if your browser has local cookies support turned off.

Create a Cookie with JavaScript

JavaScript can create, read, and delete cookies with the document.cookie property.

With JavaScript, a cookie can be created like this:

You can also add an expiry date (in UTC time). By default, the cookie is deleted when the browser is closed:

With a path parameter, you can tell the browser what path the cookie belongs to. By default, the cookie belongs to the current page.

Read a Cookie with JavaScript

With JavaScript, cookies can be read like this:

document.cookie will return all cookies in one string much like: cookie1=value; cookie2=value; cookie3=value;

Change a Cookie with JavaScript

With JavaScript, you can change a cookie the same way as you create it:

The old cookie is overwritten.

Delete a Cookie with JavaScript

Deleting a cookie is very simple.

You don’t have to specify a cookie value when you delete a cookie.

Just set the expires parameter to a past date:

You should define the cookie path to ensure that you delete the right cookie.

Some browsers will not let you delete a cookie if you don’t specify the path.

The Cookie String

The document.cookie property looks like a normal text string. But it is not.

Even if you write a whole cookie string to document.cookie, when you read it out again, you can only see the name-value pair of it.

If you set a new cookie, older cookies are not overwritten. The new cookie is added to document.cookie, so if you read document.cookie again you will get something like:

cookie1 = value; cookie2 = value;

Display All Cookies Create Cookie 1 Create Cookie 2 Delete Cookie 1 Delete Cookie 2

If you want to find the value of one specified cookie, you must write a JavaScript function that searches for the cookie value in the cookie string.

JavaScript Cookie Example

In the example to follow, we will create a cookie that stores the name of a visitor.

The first time a visitor arrives to the web page, he/she will be asked to fill in his/her name. The name is then stored in a cookie.

The next time the visitor arrives at the same page, he/she will get a welcome message.

For the example we will create 3 JavaScript functions:

1. A function to set a cookie value
2. A function to get a cookie value
3. A function to check a cookie value

A Function to Set a Cookie

First, we create a function that stores the name of the visitor in a cookie variable:

Example

function setCookie(cname, cvalue, exdays) <
const d = new Date();
d.setTime(d.getTime() + (exdays*24*60*60*1000));
let expires = «expires=»+ d.toUTCString();
document.cookie = cname + «=» + cvalue + «;» + expires + «;path=/»;
>

Example explained:

The parameters of the function above are the name of the cookie (cname), the value of the cookie (cvalue), and the number of days until the cookie should expire (exdays).

The function sets a cookie by adding together the cookiename, the cookie value, and the expires string.

A Function to Get a Cookie

Then, we create a function that returns the value of a specified cookie:

Example

function getCookie(cname) <
let name = cname + «=»;
let decodedCookie = decodeURIComponent(document.cookie);
let ca = decodedCookie.split(‘;’);
for(let i = 0; i let c = ca[i];
while (c.charAt(0) == ‘ ‘) <
c = c.substring(1);
>
if (c.indexOf(name) == 0) <
return c.substring(name.length, c.length);
>
>
return «»;
>

Function explained:

Take the cookiename as parameter (cname).

Create a variable (name) with the text to search for (cname + «=»).

Decode the cookie string, to handle cookies with special characters, e.g. ‘$’

Split document.cookie on semicolons into an array called ca (ca = decodedCookie.split(‘;’)).

If the cookie is found (c.indexOf(name) == 0), return the value of the cookie (c.substring(name.length, c.length).

If the cookie is not found, return «».

A Function to Check a Cookie

Last, we create the function that checks if a cookie is set.

If the cookie is set it will display a greeting.

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:

Example

function checkCookie() <
let username = getCookie(«username»);
if (username != «») <
alert(«Welcome again » + username);
> else <
username = prompt(«Please enter your name:», «»);
if (username != «» && username != null) <
setCookie(«username», username, 365);
>
>
>

All Together Now

Example

function setCookie(cname, cvalue, exdays) <
const d = new Date();
d.setTime(d.getTime() + (exdays * 24 * 60 * 60 * 1000));
let expires = «expires=»+d.toUTCString();
document.cookie = cname + «=» + cvalue + «;» + expires + «;path=/»;
>

function getCookie(cname) let name = cname + «=»;
let ca = document.cookie.split(‘;’);
for(let i = 0; i < ca.length; i++) let c = ca[i];
while (c.charAt(0) == ‘ ‘) c = c.substring(1);
>
if (c.indexOf(name) == 0) return c.substring(name.length, c.length);
>
>
return «»;
>

function checkCookie() let user = getCookie(«username»);
if (user != «») alert(«Welcome again » + user);
> else user = prompt(«Please enter your name:», «»);
if (user != «» && user != null) setCookie(«username», user, 365);
>
>
>

The example above runs the checkCookie() function when the page loads.

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