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Example of learning JavaScript to read and write cookies

PHPzOriginal: 2016-05-16 15:49:201180browse

This article mainly introduces the relevant knowledge points of JavaScript reading and writing cookies through examples. Friends who are in need of this can refer to it.

First of all, let us briefly understand cookies.

In the process of making web pages, we often need to transfer information from one page to another. At this time, we need to use JavaScript The cookie mechanism in . Simply put, cookies provide a convenient way to save small amounts of data on the user's computer and obtain it remotely, allowing websites to save details such as the user's habit settings or the time of the last visit to the website. The cookie itself is a short piece of information that can be saved on the user's computer by the page and then read by other pages. Cookies are generally set to expire after a certain period of time.

Of course, cookies also have limitations: browsers have limits on the number of cookies that can be saved, usually a few hundred or more. Under normal circumstances, 20 cookies are allowed per domain name, and each domain can save up to 4KB of cookies. In addition to the problems that may be caused by size restrictions, there are also many reasons that may cause cookies on the hard disk to disappear, such as reaching the expiration date. Or the user cleared the cookie information, or switched to another browser. Therefore, cookies are not suitable for storing important data. When writing code, you must also consider how to handle cookie acquisition exceptions.

In JavaScript, use the cookie attribute of the document object to store and retrieve cookies. Usually, the information in document.cookie is a string consisting of pairs of names and values, and each pair of data is in the form :

name=value;

Below we will use a simple example to show how to read and write cookies in JavaScript.

The first is createCookie.html, in which a page will be created cookie, the complete code is as follows:

<html>
<head>
  <title>createCookie</title>
  <script>
    function createCookie(){
      //get name and password
      var name = document.getElementById("name").value;
      var pwd = document.getElementById("pwd").value;
      //create cookie
      document.cookie = name+&#39;|&#39;+pwd;
      //go to showCookie.html page
      window.location.href = "showCookie.html";
    }
  </script>
</head>
<body>
  Userame:  <input id="name" type="text" /><br><br>
  Password:  <input id="pwd" type="password" /><br><br>
  <button onclick="createCookie()">Submit</submit>
</body>
</html>

A screenshot of the page is as follows:

Click the submit button and a cookie will be created. The Username and Password information is saved in it, and it will jump to the showCookie.html page. Among them, the complete code of the showCookie.html page is as follows:

<html>
<head>
  <title>showCookie</title>
  <script>
    function showCookie(){
      //document.cookie is a string, using split() function to get cookie date in array form 
      var arr = document.cookie.split(&#39;|&#39;);
      //processing data in cookie
      var cookie_info = &#39;Data in cookie:<br>username is:  &#39;+arr[0]+"<br>password is:  "+arr[1]+&#39;<br>&#39;;
      //set content of element of id "res"
      document.getElementById("res").innerHTML = cookie_info;
    }
  </script>
</head>
<body>
  <button onclick="showCookie()">Show Cookie</button>
  <p id="res"></p>
</body>
</html>

The screenshot of the page is as follows: