How to get the domain value for a cookie in JavaScript?

In JavaScript, retrieving the domain attribute value of a cookie can be achieved by parsing the document.cookie string. However, it is important to note that due to security reasons, the browser's same-origin policy restricts JavaScript from accessing cookies that do not belong to the current domain. In other words, JavaScript can only access cookies within the same domain as the current webpage and cannot directly retrieve the domain attribute of a cookie.

Implementation Steps

1. Read all cookies under the current domain: Using document.cookie retrieves all accessible cookies under the current domain, returning a string where each cookie is separated by a semicolon and space.

2. Parse the cookie string: Split the string obtained from document.cookie using a semicolon and space to get individual key-value pairs.

3. Retrieve the value of a specific cookie: Iterate through the split array to find the desired cookie key and extract its value.

Example Code

Below is an example code snippet demonstrating how to read and parse the cookie string in JavaScript to retrieve the value of a specific cookie:

javascript
function getCookieValue(cookieName) {
    const allCookies = document.cookie; // Get all accessible cookies under the current domain as a string
    const cookiesArray = allCookies.split('; '); // Split into an array of individual cookies

    for (let i = 0; i < cookiesArray.length; i++) {
        const cookiePair = cookiesArray[i].split('='); // Split key and value

        if (cookiePair[0] === cookieName) {
            return cookiePair[1]; // Return the value when the cookie name matches
        }
    }

    return null; // Return null if the specified cookie is not found
}

// Example: Assuming a cookie named 'session_id'
const sessionId = getCookieValue('session_id');
console.log('Session ID:', sessionId);

Note

The above method cannot retrieve other cookie attributes such as Domain, Path, or expiration time (Expires/Max-Age). These attributes are not included in document.cookie due to security considerations. If you need to check these attributes on the server side, you should do so on the server side, such as by setting and checking these cookie attributes in HTTP response headers.