A URL consists of four parts, take www.2cto.com as an example (the default port for http is 80, and the default port for https is 443. If it is the default port, it can be omitted, so this URL is equivalent to www.2cto.com: 80
Protocol: http
Host: www.2cto.com
Port: 80
Path:/
The so-called same origin means that the protocol, host and port of this URL are generally the same. Domain or domain is also the concept of source here.
For the above URL, there are the following results:
'
There is an exception, javascript can modify the value of the host and port parts by setting document.domain, if In this way, the set value will be used as the standard for same-origin policy check. For example, for http://blog.csdn.net/yanical and http://bbs.csdn.net/, you can execute the following javascript:
[ javascript] document.domain = "csdn.net";
After this, the two pages have the same source. For security reasons, they cannot be set to other main domains, such as http://www.csdn. net/ cannot be set to sina.com
We see that only the host part is set in the javascript, and the port part is not mentioned. In fact, when the above javascript is executed, the port is also set, and is set to a null value. Therefore, if the above javascript is executed for both http://blog.csdn.net:81/yanical and http://blog.csdn.net/yanical, the ports will be set to null. They also become homologous.
The same origin policy was first used to prevent js from one source from obtaining or modifying the document attributes of another source. The source of javascript here refers to the source of the HTML page that loads javascript. Rather than the source where the javascript itself is located.
For example, there are two HTML and two javascript. test.html contains an iframe that references frame.html, and they are in different sources; test.html also references two js, one of them is also different from the source of test.html; the javascript of test.html also tries to modify frame.html
test.html:
[html]
<script> <br/>document.write( '------write from test.html'); <br/>alert(document.getElementById('vFrame').contentDocument.body.innerHTML='------overwrite frame from test.html'; <br/>< ;/script> <br/> <br/> <br/>frame.html:<br/> <br/>[html] <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <br/><html> <br/> <head> <br/> <br/><body> <br/><script> <br/>document.write('------write from frame.html'); <br/></script>
body>

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.


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