Not Modified The client has buffered documents and issued a conditional request (usually providing an If-Modified-Since header to indicate that the client only wants documents that are newer than the specified date). The server tells the client that the original buffered document can continue to be used.
If the client finds that the cached file has Last Modified when requesting a file, then the request will include If Modified Since , and this time is the Last Modified of the cached file. Therefore, if the request contains If Modified Since, it means that it is already cached on the client. Just judge this time and the modification time of the currently requested file to determine whether to return 304 or 200. For static files, such as CSS and images, the server will automatically compare Last Modified and If Modified Since to complete caching or updating. But for dynamic pages, which are dynamically generated pages, they often do not contain Last Modified information, so browsers, gateways, etc. will not cache them, that is, a 200 request will be completed every time they are requested.
Therefore, for caching acceleration of dynamic pages, you must first add the Last Modified definition to the HTTP Header of the Response, and then return 200 or 304 based on the If Modified Since in the Request and the update time of the requested content. Although a database query has been made when returning 304, more subsequent database queries can be avoided, and no page content is returned but only an HTTP header, thus greatly reducing bandwidth consumption and improving user experience.
When these caches are valid, viewing a request through HttpWatch will yield the following results:
First visit 200
Second access by mouse click (Cache)
Press F5 to refresh 304
Press Ctrl F5 to force refresh 200
If this is the case, it means that the cache is really effective. The above is my understanding of HTTP 304.

JavaScript's application in the real world includes front-end and back-end development. 1) Display front-end applications by building a TODO list application, involving DOM operations and event processing. 2) Build RESTfulAPI through Node.js and Express to demonstrate back-end applications.

The main uses of JavaScript in web development include client interaction, form verification and asynchronous communication. 1) Dynamic content update and user interaction through DOM operations; 2) Client verification is carried out before the user submits data to improve the user experience; 3) Refreshless communication with the server is achieved through AJAX technology.

Understanding how JavaScript engine works internally is important to developers because it helps write more efficient code and understand performance bottlenecks and optimization strategies. 1) The engine's workflow includes three stages: parsing, compiling and execution; 2) During the execution process, the engine will perform dynamic optimization, such as inline cache and hidden classes; 3) Best practices include avoiding global variables, optimizing loops, using const and lets, and avoiding excessive use of closures.

Python is more suitable for beginners, with a smooth learning curve and concise syntax; JavaScript is suitable for front-end development, with a steep learning curve and flexible syntax. 1. Python syntax is intuitive and suitable for data science and back-end development. 2. JavaScript is flexible and widely used in front-end and server-side programming.

Python and JavaScript have their own advantages and disadvantages in terms of community, libraries and resources. 1) The Python community is friendly and suitable for beginners, but the front-end development resources are not as rich as JavaScript. 2) Python is powerful in data science and machine learning libraries, while JavaScript is better in front-end development libraries and frameworks. 3) Both have rich learning resources, but Python is suitable for starting with official documents, while JavaScript is better with MDNWebDocs. The choice should be based on project needs and personal interests.

The shift from C/C to JavaScript requires adapting to dynamic typing, garbage collection and asynchronous programming. 1) C/C is a statically typed language that requires manual memory management, while JavaScript is dynamically typed and garbage collection is automatically processed. 2) C/C needs to be compiled into machine code, while JavaScript is an interpreted language. 3) JavaScript introduces concepts such as closures, prototype chains and Promise, which enhances flexibility and asynchronous programming capabilities.

Different JavaScript engines have different effects when parsing and executing JavaScript code, because the implementation principles and optimization strategies of each engine differ. 1. Lexical analysis: convert source code into lexical unit. 2. Grammar analysis: Generate an abstract syntax tree. 3. Optimization and compilation: Generate machine code through the JIT compiler. 4. Execute: Run the machine code. V8 engine optimizes through instant compilation and hidden class, SpiderMonkey uses a type inference system, resulting in different performance performance on the same code.

JavaScript's applications in the real world include server-side programming, mobile application development and Internet of Things control: 1. Server-side programming is realized through Node.js, suitable for high concurrent request processing. 2. Mobile application development is carried out through ReactNative and supports cross-platform deployment. 3. Used for IoT device control through Johnny-Five library, suitable for hardware interaction.


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