Skip to content

Writing Cookies

Writing Cookies

Introduction

Set cookies by assigning to document.cookie. Each assignment creates or updates a single cookie.

Basic Writing

// Set a cookie (key=value)
document.cookie = 'theme=dark';

document.cookie = 'session=abc123; path=/; max-age=86400; Secure; SameSite=Strict';

// Options:
// path=/       — Available on all paths
// max-age=86400 — Expires in 24 hours (seconds)
// Secure       — Only over HTTPS
// SameSite=Strict — Block cross-site requests
// domain=.example.com — Share with subdomains

Using Expires

// Set expiration date
const expires = new Date();
expires.setDate(expires.getDate() + 7); // 7 days from now
document.cookie = `premium=true; expires=${expires.toUTCString()}; path=/`;

Summary

document.cookie = 'key=value' sets a cookie
Append options after the value: ; path=/; max-age=86400
Secure flag restricts to HTTPS only
SameSite=Strict prevents CSRF attacks
max-age sets expiration in seconds

Further Reading

MDN: document.cookie