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Selected Reading
How to create domain-based cookies using JavaScript?
To create a domain-based cookie, set the domain and path attribute on your cookie. Domain-based cookies are accessible across all subdomains of the specified domain.
Syntax
document.cookie = "cookieName=value; domain=.example.com; path=/";
Domain Cookie Format
domain=.example.com
The dot prefix (.) makes the cookie available to all subdomains like www.example.com, api.example.com, etc.
Example: Setting Domain-Based Cookie
<html>
<head>
<script>
function WriteCookie() {
if( document.myform.customer.value == "" ){
alert("Enter some value!");
return;
}
cookievalue = escape(document.myform.customer.value) + ";";
document.cookie = "name=" + cookievalue +
"domain=.example.com;path=/";
document.write("Setting Cookies : " + "name=" + cookievalue);
}
</script>
</head>
<body>
<form name="myform" action="">
Enter name: <input type="text" name="customer"/>
<input type="button" value="Set Cookie" onclick="WriteCookie();"/>
</form>
</body>
</html>
Modern Approach Using JavaScript
function setDomainCookie(name, value, domain) {
const expires = new Date();
expires.setTime(expires.getTime() + (7 * 24 * 60 * 60 * 1000)); // 7 days
document.cookie = `${name}=${value}; expires=${expires.toUTCString()}; domain=${domain}; path=/`;
console.log(`Cookie set: ${name}=${value} for domain ${domain}`);
}
// Usage
setDomainCookie("username", "john_doe", ".example.com");
setDomainCookie("preferences", "dark_mode", ".mysite.com");
Cookie set: username=john_doe for domain .example.com Cookie set: preferences=dark_mode for domain .mysite.com
Key Points
-
Domain prefix: Use
.example.com(with dot) for all subdomains -
Without dot:
example.comworks only for the exact domain -
Path: Set
path=/to make cookie available site-wide -
Security: Add
SecureandSameSiteattributes for production
Reading Domain Cookies
function getCookie(name) {
const cookies = document.cookie.split(';');
for(let cookie of cookies) {
const [cookieName, cookieValue] = cookie.trim().split('=');
if(cookieName === name) {
return cookieValue;
}
}
return null;
}
// Read the domain cookie
const username = getCookie("username");
console.log("Username from cookie:", username);
Username from cookie: john_doe
Conclusion
Domain-based cookies use the domain attribute to share data across subdomains. Always include the dot prefix and set appropriate path and security attributes for production use.
Updated on: 2026-03-15T23:18:59+05:30
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