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1. What do HTTP status codes know?

Answer: 100 Continue, generally when sending a post request, the server will return this message after sending the http header, indicating confirmation, and then send specific parameter information.

200 OK OK Return message

201 Created Request succeeded and the server created a new resource

202 Accepted The server has accepted the request but has not yet processed it.

301 Moved Permanently The requested page has been permanently moved to a new location.

302 Found Temporary redirection.

303 See Other Temporary redirects, and always use GET to request a new URI.

304 Not Modified The requested page has not been modified since the last request.

400 Bad Request The server does not understand the format of the request and the client should not attempt to make a request with the same content again.

401 Unauthorized The request is not authorized.

403 Forbidden Forbidden Access denied.

404 Not Found No resource was found to match the URI.

500 Internal Server Error The most common server-side error.

503 Service Unavailable The server is temporarily unable to process the request (possibly due to overload or maintenance).

2. What performance optimization methods do you have?

A: (1) Reduce the number of http requests: CSS Sprites, JS, CSS source code compression, image size control is appropriate; web page Gzip, CDN hosting, data cache, image server.

(2)Front template JS+ data, reduce bandwidth waste caused by HTML tags, front variables to save AJAX request results, each operation of local variables, no request, reduce the number of requests

(3)Use innerHTML instead of DOM operations to reduce DOM operations and optimize java performance.

(4)When there are many styles to be set, set className instead of directly operating style.

(5)Use fewer global variables and cache DOM node lookup results. Reduce IO read operations.

(6)Avoid CSS _Expressions, also known as Dynamic properties.

(7)Picture preloading, style sheets at the top and scripts at the bottom with timestamps.

3. What is elegant degradation and gradual enhancement?

A: Graceful degradation: Web sites work fine in all modern browsers, but if users are using older browsers, the code checks to make sure they work fine. Due to IE's unique box model layout, hacks for different versions of IE have been gracefully degraded, adding candidates for browsers that can't support features that degrade the experience in some way on older browsers without completely failing.

Progressive enhancement: Start with basic features supported by all browsers, gradually add features that are only supported by newer browsers, and add additional styles and features to the page that are not harmful to the base browser. When supported by the browser, they will automatically appear and function.

From a logical point of view, multithreading means that multiple execution parts of an application can be executed simultaneously. But the operating system does not treat multiple threads as separate applications for scheduling and managing processes and allocating resources. This is an important distinction between processes and threads.

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