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How to clear cookies in javascript

青灯夜游Original: 2021-06-17 14:31:5611099browse

Clear method: Do not specify a cookie value, just set the expires parameter to a past date, the syntax is "document.cookie="username=;expires=Thu,01 Jan 1970 00:00:00 UTC;path ==;";".

The operating environment of this tutorial: windows7 system, javascript version 1.8.5, Dell G3 computer.

Cookies provide a useful way for web applications to save information about users. For example, when a user visits our site, cookies can be used to save user preferences or other information so that the next time the user visits our site, the application can retrieve the previously saved information.

What the heck is Cookie

Cookie is a small piece of text information that accompanies user requests and pages Passed between web server and browser. The information contained in the cookie can be read by the web application each time the user visits the site.

Cookies appear to solve the problem of saving user information. For example

When a user visits a web page, the user's name can be stored in a cookie.

The next time the user visits the page, the cookie will remember the username.

Cookies can remember user information across all web pages. It contains information in the form of a string and is saved in the form of key-value pairs, that is, in the key=value format. Each cookie is usually separated by ";".

username = Daisy Green

Composition of Cookie

##Cookie in HTTP In the header information, the header format of HTTP Set-Cookie is as follows:

Set-Cookie: name=value; [expires=date]; [path=path];
[domain=domainname]; [secure];

A specific example in the HTTP code:

<meta http-equiv="set-cookie" content=" cookieName = cookieValue;expires=01-Dec-2006 01:14:26 GMT; path=/" />

As can be seen from the above format, Cookie It consists of the following parts.

Name/Value pairs

Name/Value are separated by semicolons. There are at most 20 pairs in a cookie. Each web page has at most one cookie. The length of Value does not exceed 4K. For Value values, it is best to encode them with encodeURIComponent.

JS Cookie

In JS, you can use the cookie attribute of the Document object to manipulate cookies. JS can read, create, modify and delete the cookies of the current web page. Let’s take a look at the specific operations.

Create Cookie

JS can use the document.cookie attribute to create cookies. Cookies can be created in the following ways:

document.cookie = "username=Daisy Green";

You can also add Valid date (UTC time). By default, cookies are deleted when the browser is closed:

document.cookie = "username=Daisy Green; expires=Mon, 26 Aug 2019 12:00:00 UTC";

Through the path parameter, you can tell the browser what path the cookie belongs to. By default, the cookie belongs to the current page.

document.cookie = "username=Daisy Green; expires=Mon, 26 Aug 2019 12:00:00 UTC"; path=/";

Read Cookie

Through JS, you can read the cookie like this:

var x = document.cookie;

document.cookie All cookies will be returned in a string, for example: cookie1=value; cookie2<span style="font-family: " microsoft yahei sans gb helvetica neue tahoma arial sans-serif></span><br>

Example:

<html>
  <head>  
   <script type = "text/javascript">
     <!--
      function ReadCookie() {
        var allcookies = document.cookie;
        document.write ("All Cookies : " + allcookies );
        
        // Get all the cookies pairs in an array
        cookiearray = allcookies.split(&#39;;&#39;);
        
        // Now take key value pair out of this array
        for(var i=0; i<cookiearray.length; i++) {
         name = cookiearray[i].split(&#39;=&#39;)[0];
         value = cookiearray[i].split(&#39;=&#39;)[1];
         document.write ("Key is : " + name + " and Value is : " + value);
        }
      }
     //-->
   </script>   
  </head>
  
  <body>   
   <form name = "myform" action = "">
     <p> click the Button to View Result:</p>
     <input type = "button" value = "Get Cookie" onclick = "ReadCookie()"/>
   </form>   
  </body>
</html>

Run:

Change cookie

By using JS, we can change it just like creating a cookie:

document.cookie = "username=Steve Jobs; expires=Sun, 31 Dec 2017 12:00:00 UTC; path=/";

This old The cookie will be overwritten.

Example:

<html>
  <head>  
   <script type = "text/javascript">
     <!--
      function WriteCookie() {
        var now = new Date();
        now.setMonth( now.getMonth() + 1 );
        cookievalue = escape(document.myform.customer.value) + ";"
        
        document.cookie = "name=" + cookievalue;
        document.cookie = "expires=" + now.toUTCString() + ";"
        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>

Run:

How to clear cookies in javascript

##Delete cookie

##Delete Cookies are very simple, there is no need to specify a cookie value: just set the expires parameter to a past date:

document.cookie = "username=; expires=Thu, 01 Jan 1970 00:00:00 UTC; path=/;";

<br>The cookie path should be defined to ensure that the correct cookie is deleted. If the path is not specified, some browsers will not let us delete cookies.

Example:

<html>
  <head>  
   <script type = "text/javascript">
     <!--
      function WriteCookie() {
        var now = new Date();
        now.setMonth( now.getMonth() - 1 );
        cookievalue = escape(document.myform.customer.value) + ";"
        
        document.cookie = "name=" + cookievalue;
        document.cookie = "expires=" + now.toUTCString() + ";"
        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>

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