Read and write cookie code in JavaScript

Handling cookies in JavaScript is a bit complicated because of its notoriously crappy interface, namely the BOM's document.cookie property. What's unique about this property is that it behaves differently depending on how it's used. When used to obtain attribute values, document.cookie returns the strings of all cookies available to the current page (based on the cookie's domain, path, expiration time, and security settings), as a series of semicolon-separated name-value pairs, as in the following example Shown:

name1=value1;name2=value2;name3=value3;

1 All names and values ​​are URL encoded, so they must be decoded using decodeURIComponent().

When used for settings, the document.cookie attribute can be set to a new cookie string. This cookie string will be interpreted and added to the existing cookie collection. Setting document.cookie does not overwrite the cookie unless the cookie named already exists. The format for setting cookies is as follows, the same format used in the set-Cookie header:

name=value; expires=expiration_time; path=domian_path; domian=domain_nam

Among these parameters, only the name and value of the cookie are necessary. Here is a simple example:

document.cookie = "name=Nicholas";

　This code creates a cookie called name with the value Nicholas. This cookie will be sent every time the client sends a request to the server; it will be deleted when the browser is closed. Although this code is fine, because neither the name nor the value needs to be encoded, it is best to use it like the example below every time you set a cookie

encodeURIComponent();

　document.cookie = encodeURIComponent ("name") + "=" + encodeURIComponent("Nicholas");

　 To specify additional information for the created cookie, just append parameters to the string, in the same format as the Set-Cookie header, as follows ：

document.cookie = encodeURIComponent("name") + "=" + encodeURIComponent("Nicholas") + "; domain=.wrox.com; path=/";

Due to JavaScript Reading and writing cookies is not very intuitive. We often write some functions to simplify the functionality of cookies. There are three basic cookie operations: read, write and delete. They are represented in the CookieUtil object as follows:

var CookieUtil = {
    get: function (name) {
        var cookieName = encodeURIComponent(name) + "=",
            cookieStart = document.cookie.indexOf(cookieName),
            cookieValue = null;
        if (cookieStart > -1) {
            var cookieEnd = document.cookie.indexOf(";", cookieStart)
            if (cookieEnd == -1) {
                cookieEnd = document.cookie.length;
            }
            cookieValue = decodeURIComponent(document.cookie.substring(cookieStart + cookieName.length, cookieEnd));
        }
        return cookieValue;
    },
    set: function (name, value, expires, path, domain, secure) {
        var cookieText = encodeURIComponent(name) + "=" + encodeURIComponent(value);
        if (expires instanceof Date) {
            cookieText += "; expires=" + expires.toGMTString();
        }
        if (path) {
            cookieText += "; path=" + path;
        }
        if (domain) {
            cookieText += "; domain=" + domain;
        }
        if (secure) {
            cookieText += "; secure";
        }
        document.cookie = cookieText;
    },
    unset: function (name, path, domain, secure) {
        this.set(name, "", new Date(0), path, domain, secure);
    }
};

CookieUtil.get() method gets the corresponding value based on the name of the cookie. He does this by looking for the cookie name plus the equal sign in the document.cookie string. If found, then use indexOf() to find the first semicolon after the position (indicating the end position of the cookie). If no semicolon is found, it means that the cookie is the last one in the string, and the strings under the domain are all cookie values. The value is decoded using decodeURIComponent() and finally returned. If no cookie is found, null is returned.
The CookieUtil.set() method sets a cookie on the page and accepts several parameters: cookie name, cookie value, optional Date object used to specify when the cookie should be deleted, and optional URL of the cookie Path, optional fields, and optional Boolean value indicating whether to add the secure flag. The parameters are ordered according to how frequently they are used, only the first two are required. In this method, both the name and value are URL-encoded using encodeURIComponent() and other options are checked. If the expires parameter is a Date object, the Date object's toGMTString() method will be used to correctly format the Date object and be added to the expires option. The other part of the method is to construct the cookie string and set it into document.cookie.
There is no direct way to delete existing cookies. So, set the cookie again using the same path, domain, and security options, and set the expiration time to the past. The CookieUtil.unset() method can handle this kind of thing. It accepts 4 parameters: the name of the cookie to be deleted, an optional path parameter, an optional domain parameter, and an optional security parameter. These parameters plus an empty string and set the expiration time to January 1, 1970 (the value of the Date object initialized to 0ms) are passed to CookieUtil.set(). This ensures that the cookie is deleted.
These methods can be used as follows:

//设置cookie
CookieUtil.set("name", "Nicholas");
CookieUtil.set("book", "Professional <a href="http://www.php1.cn/">JavaScript</a>");
//读值
alert(CookieUtil.get("name"));
alert(CookieUtil.get("book"));
//删除cookie
CookieUtil.unset("name");
CookieUtil.unset("book")
//设置1个cookie，包括它的路径、域、截止日期
CookieUtil.set("name", "Nicholas", "/books/projs/", "www.wrox.com", new Date("January 1, 2010"));
//删除同一cookie
CookieUtil.unset("name", "/books/projs/", "www.wrox.com");
//设置1个<a href="http://www.php1.cn/category/23.html">安全</a>cookie
CookieUtil.set("name", "Nicholas", null, null, null, true);

These methods make it easier to use cookies to store data on the client side by handling the task of parsing and constructing cookie strings