Detailed explanation of ajax and jsonp cross-domain (with code)
This time I will bring you a detailed explanation of ajax and jsonp cross-domain (with code), what are the precautions for implementing ajax and jsonp cross-domain, the following is a practical case, let's take a look.
Why are there cross-domain problems? - Because there is a same-origin policy
The same-origin policy is a security policy of the browser. The so-called same-origin refers to the protocol in the request URL address, the domain name and the port are the same, as long as One of the differences is cross-domain
The same origin policy is mainly to ensure the security of the browser
Under the same origin policy, the browser does not allow Ajax to obtain server data across domains
http://www.example.com/detail.html
Cross-domain request:
http://api. example.com/detail.html The domain name is different
http://www.example.com:8080/detail.html The port is different
http://api.example.com:8080/detail.html The domain name and port are different
https://api.example.com/detail.html The protocol and domain name are different
https://www.example.com:8080/detail.html The ports and protocols are different
ajaxBasic concepts
To understand this concept, you must first know synchronous interaction and asynchronous interaction
Synchronous interaction: client browsing The server sends a request to the server, and the server returns a page. The returned page will overwrite the previous page. We call this interaction method synchronous interaction
Asynchronous interaction: it can The browser will send a request to the server, and the server will return the data. The returned data will not overwrite the previous page. We call this interaction method asynchronous interaction
ajax Main application scenarios: Dynamic data interaction with the server can be performed without refreshing the page
Principle of interaction
Synchronous interaction principle: How do we send a request to the server in the browser? You can click a hyperlink, submit a form, and enter an address in the browser address bar, all of which are sending requests to the server. In fact, the browser helps us send requests to the server
The principle of asynchronous interaction : JavaScript provides us with a new API interface to help us send http requests. The XMLHttpRequest object helps us send requests.
All our interactive operations can be done through this object. Complete, send the request, and accept the data from the server
Specific application scenarios of ajax
The front desk can send it to the server through XMLHttpRequest Send a request, then accept the data returned by the server through the XMLHttpRequest object, and finally write the data to the page through dom operations
ajax: can be used for form input specification verification
ajax: It can also be used for performance optimization. For example, if a page is very large and it is impossible to load it in one go, a rolling load can be achieved
Four steps of XMLHttpRequest interaction
1. Instantiate the XMLHttpRequest object
2. If you want to interact with the server, you must interact with The server opens a connection
3. Send data to the server and parameter data to the server
4. Accept the data returned by the server. The server will return some status when returning to the client. You can pass Monitor server status changes to better control the entire interaction process
ajax cross-domain
Cross-domain: Suppose I visit a site, The background returns me a page, and then I want to access the resources of site B on this page of site A. This is a cross-domain effect. Cross-domain browsers have security restrictions
Solution·Cross-domain method: jsonp method
The full name of JSONP is JSON with Padding, which is based on the JSON format and is generated to solve cross-domain request resources. s solution. The basic principle of its implementation is to use the <script></script> element tag in HTML to remotely call the JSON file to achieve data transfer. If you want to get the JSON data (getUsers.JSON) that exists in b.com under the a.com domain:
The essential principle of jsonp solving cross-domain issues: Because browsers have same origin restrictions, different sites cannot communicate with each other. Access, but sometimes we just want to get data from other sites, such as adding Weather Forecast data where we want to get quick data. This must be cross-domain, so what should we do?
Principle: It is to dynamically create the <script> tag, and then use the src of <script> to obtain cross-domain data without being subject to the same-origin policy. </script>
In this way, the background can obtain the callback function passed from the front desk, and finally the background returns the call of this function, and the parameters are the data requested by the front desk
jscode
<script> function handleResponse(response){ console.log(response); } </script> <script> window.onload = function() { var oBtn = document.getElementById('btn'); oBtn.onclick = function() { var script = document.createElement("script"); script.src = "https://api.douban.com/v2/book/search?q=javascript&count=1&callback=handleResponse"; document.body.insertBefore(script, document.body.firstChild); }; }; </script>
I believe you have mastered the method after reading the case in this article. For more exciting information, please pay attention to other related articles on the php Chinese website!
Recommended reading:
How to obtain json data through ajax across domains
When the ajax request error status code is 0 How to deal with it
The above is the detailed content of Detailed explanation of ajax and jsonp cross-domain (with code). For more information, please follow other related articles on the PHP Chinese website!

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.

C and C play a vital role in the JavaScript engine, mainly used to implement interpreters and JIT compilers. 1) C is used to parse JavaScript source code and generate an abstract syntax tree. 2) C is responsible for generating and executing bytecode. 3) C implements the JIT compiler, optimizes and compiles hot-spot code at runtime, and significantly improves the execution efficiency of JavaScript.


Hot AI Tools

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Undress AI Tool
Undress images for free

Clothoff.io
AI clothes remover

Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Article

Hot Tools

PhpStorm Mac version
The latest (2018.2.1) professional PHP integrated development tool

mPDF
mPDF is a PHP library that can generate PDF files from UTF-8 encoded HTML. The original author, Ian Back, wrote mPDF to output PDF files "on the fly" from his website and handle different languages. It is slower than original scripts like HTML2FPDF and produces larger files when using Unicode fonts, but supports CSS styles etc. and has a lot of enhancements. Supports almost all languages, including RTL (Arabic and Hebrew) and CJK (Chinese, Japanese and Korean). Supports nested block-level elements (such as P, DIV),

MinGW - Minimalist GNU for Windows
This project is in the process of being migrated to osdn.net/projects/mingw, you can continue to follow us there. MinGW: A native Windows port of the GNU Compiler Collection (GCC), freely distributable import libraries and header files for building native Windows applications; includes extensions to the MSVC runtime to support C99 functionality. All MinGW software can run on 64-bit Windows platforms.

MantisBT
Mantis is an easy-to-deploy web-based defect tracking tool designed to aid in product defect tracking. It requires PHP, MySQL and a web server. Check out our demo and hosting services.

EditPlus Chinese cracked version
Small size, syntax highlighting, does not support code prompt function
