JavaScript Cookies

As HTTP is a stateless protocol i.e. all requests to the server are treated as new requests and there is no way to determine if a request comes from a user who already did a request before or if it is a new user.

A cookie is a small piece of information that the server stores in the client browser to recognize the user in the future. A cookie is sent every time, the same client sends a request to the server. JavaScript facilitates the features of both creating and retrieving cookie values.

How do cookies work in JavaScript?

When a request comes to the server, the application can attach a small information calls a cookie in response. If the client’s browser accepts the cookie then it stores this information on the client’s machine as plain text. When the client sends a new request browser will attach this information to the server with the request. The application can retrieve the cookie and can identify the user or client.

Restrictions of cookies

  • A cookie can store a maximum of 4 kb of data.
  • Cookies are specific to the domain.
  • A browser can store max 20 cookies per domain.

To Create a Cookie:

document.cookie = "key = value";

To Retrieve a Cookie:



<!DOCTYPE html>
<input type="button" value="set" onclick="setCookie()">
<input type="button" value="get" onclick="getCookie()">
function setCookie()
document.cookie="username=John Miller";
function getCookie()
var array=document.cookie.split("=");
alert("Name="+array[0]+" "+"Value="+array[1]);
alert("No cookie available");

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