1. Simple comparison of various storage solutions
Cookies: supported by all browsers, capacity is 4KB
UserData: only supported by IE, capacity is 64KB
Flash: 100KB, non-HTML native, requires plug-in support
Google Gears SQLite: requires plug-in support, unlimited capacity
LocalStorage: HTML5, capacity is 5M
SesstionStorage: HTML5, capacity is 5M
globalStorage: unique to Firefox, Firefox13 no longer supports this method
UserData is only supported by IE , Google Gears SQLite requires plug-ins, and Flash has gradually withdrawn from the stage of history with the emergence of HTML5, so today our protagonists are only three of them: Cookie, LocalStorge, SessionStorge;
2. Cookie
As a front-end that deals with Cookies The number of times will definitely not be less. Cookie is a relatively old technology. In 1993, Netscape employee Lou Montulli invented today's widely used cookies in order to further improve the access speed when users visit a website, and at the same time to further realize a personalized network. Cookies used.
2.1 Characteristics of Cookies
Let’s first look at the characteristics of Cookies:
1) The size of cookies is limited. The cookie size is limited to 4KB and cannot accept big data like large files or emails.
2) As long as there is a request involving cookies, cookies will be sent back and forth between the server and the browser (this explains why local files cannot test cookies). Moreover, the cookie data is always carried in the http request from the same origin (even if it is not needed), which is also an important reason why the cookie cannot be too large. Orthodox cookie distribution is achieved by extending the HTTP protocol. The server adds a special line of instructions to the HTTP response header to prompt the browser to generate the corresponding cookie according to the instructions.
3) Every time a user requests server data, cookies will be sent to the server along with these requests. Server scripting languages such as PHP can process the data sent by cookies, which can be said to be very convenient. Of course, the front end can also generate cookies. Using js to operate cookies is quite cumbersome. The browser only provides an object such as document.cookie, and assigning and obtaining cookies is more troublesome. In PHP, we can set cookies through setcookie() and obtain cookies through the super-global array $_COOKIE.
The content of cookie mainly includes: name, value, expiration time, path and domain. The path and domain together form the scope of the cookie. If the expiration time is not set, it means that the lifetime of this cookie is during the browser session. When the browser window is closed, the cookie disappears. This type of cookie that lasts for the duration of the browser session is called a session cookie. Session cookies are generally not stored on the hard disk but in memory. Of course, this behavior is not specified by the specification. If an expiration time is set, the browser will save the cookies to the hard disk. If you close and open the browser again, these cookies will still be valid until the set expiration time is exceeded. Cookies stored on the hard drive can be shared between different browser processes, such as two IE windows. Different browsers have different processing methods for cookies stored in memory.
2.2 Session
When it comes to cookies, we can’t help but talk about Session.
Session mechanism. The session mechanism is a server-side mechanism. The server uses a structure similar to a hash table (or may use a hash table) to save information. When the program needs to create a session for a client's request, the server first checks whether the client's request already contains a session identifier (called session id). If it does, it means that a session has been created for this client before. , the server will retrieve the session according to the session id and use it (if it cannot be retrieved, a new one will be created). If the client request does not contain the session id, a session will be created for the client and a session id associated with this session will be generated. , the value of the session id should be a string that is neither repeated nor easy to find patterns to imitate. This session id will be returned to the client in this response for storage. The method of saving this session ID can use cookies, so that during the interaction process, the browser can automatically send this identification to the server according to the rules. Generally, the name of this cookie is similar to SEEESIONID. But cookies can be artificially disabled, and there must be other mechanisms to still pass the session id back to the server when cookies are disabled. A frequently used technique is called URL rewriting, which appends the session id directly to the end of the URL path. For example: http://damonare.cn?sessionid=123456 There is also a technology called form hidden fields. That is, the server will automatically modify the form and add a hidden field so that the session id can be passed back to the server when the form is submitted. For example:

JavaScript runs in browsers and Node.js environments and relies on the JavaScript engine to parse and execute code. 1) Generate abstract syntax tree (AST) in the parsing stage; 2) convert AST into bytecode or machine code in the compilation stage; 3) execute the compiled code in the execution stage.

The future trends of Python and JavaScript include: 1. Python will consolidate its position in the fields of scientific computing and AI, 2. JavaScript will promote the development of web technology, 3. Cross-platform development will become a hot topic, and 4. Performance optimization will be the focus. Both will continue to expand application scenarios in their respective fields and make more breakthroughs in performance.

Both Python and JavaScript's choices in development environments are important. 1) Python's development environment includes PyCharm, JupyterNotebook and Anaconda, which are suitable for data science and rapid prototyping. 2) The development environment of JavaScript includes Node.js, VSCode and Webpack, which are suitable for front-end and back-end development. Choosing the right tools according to project needs can improve development efficiency and project success rate.

Yes, the engine core of JavaScript is written in C. 1) The C language provides efficient performance and underlying control, which is suitable for the development of JavaScript engine. 2) Taking the V8 engine as an example, its core is written in C, combining the efficiency and object-oriented characteristics of C. 3) The working principle of the JavaScript engine includes parsing, compiling and execution, and the C language plays a key role in these processes.

JavaScript is at the heart of modern websites because it enhances the interactivity and dynamicity of web pages. 1) It allows to change content without refreshing the page, 2) manipulate web pages through DOMAPI, 3) support complex interactive effects such as animation and drag-and-drop, 4) optimize performance and best practices to improve user experience.

C and JavaScript achieve interoperability through WebAssembly. 1) C code is compiled into WebAssembly module and introduced into JavaScript environment to enhance computing power. 2) In game development, C handles physics engines and graphics rendering, and JavaScript is responsible for game logic and user interface.

JavaScript is widely used in websites, mobile applications, desktop applications and server-side programming. 1) In website development, JavaScript operates DOM together with HTML and CSS to achieve dynamic effects and supports frameworks such as jQuery and React. 2) Through ReactNative and Ionic, JavaScript is used to develop cross-platform mobile applications. 3) The Electron framework enables JavaScript to build desktop applications. 4) Node.js allows JavaScript to run on the server side and supports high concurrent requests.

Python is more suitable for data science and automation, while JavaScript is more suitable for front-end and full-stack development. 1. Python performs well in data science and machine learning, using libraries such as NumPy and Pandas for data processing and modeling. 2. Python is concise and efficient in automation and scripting. 3. JavaScript is indispensable in front-end development and is used to build dynamic web pages and single-page applications. 4. JavaScript plays a role in back-end development through Node.js and supports full-stack development.


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