How to use JavaScript to manipulate browser cookies?

How to use JavaScript to operate browser cookies?

With the development of the Internet, Cookie has become one of the commonly used technologies in Web development. It can store some information about the user in order to share the data between multiple requests from the user. By using JavaScript, we can easily operate browser cookies. This article will introduce how to use JavaScript to create, read, update and delete cookies, and provide corresponding code examples.

1. Create Cookie
   To create a Cookie, we need to use the cookie attribute of the document object to set the Cookie value in the format of "key=value". The following is an example:

document.cookie = "username=John Doe";

This creates a cookie named "username" with the value "John Doe" in the browser.

2. Read Cookie
   To read a Cookie, we can use the cookie attribute of the document object to obtain all Cookies, and then use the string related methods to parse the required Cookie value. Here is an example:

var allCookies = document.cookie;
var cookiesArray = allCookies.split("; "); // 将所有的Cookie分割成一个数组

for (var i = 0; i < cookiesArray.length; i++) {
    var cookie = cookiesArray[i];
    var cookiePair = cookie.split("="); // 将键值对分割
    var key = cookiePair[0];
    var value = cookiePair[1];
    
    console.log(key + ": " + value);
}

This code will output all Cookie key-value pairs.

3. Update Cookie
   To update a cookie, we only need to reset the cookie with the same name. Here is an example:

document.cookie = "username=Jane Smith";

This will update the value of the cookie named "username" from "John Doe" to "Jane Smith".

4. Delete Cookie
   To delete a cookie, we only need to set the expiration time of the corresponding cookie to a time in the past. The following is an example:

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

This will delete the cookie named "username".

It should be noted that when using JavaScript to operate cookies, you need to ensure that the code is running on the page related to the cookie and needs to comply with the same origin policy. In addition, since cookies are stored on the client side, there may be some security risks, especially when sensitive information is stored. To ensure the security of cookies, you can use the secure flag and the HttpOnly flag.

To sum up, it is very simple to use JavaScript to operate browser cookies. By creating, reading, updating and deleting cookies, we can flexibly store and share user information in web development. We hope that the code examples provided in this article can help readers better understand and apply Cookie technology.

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