Introduction to the use of global function each in jquery_jquery
jquery contains two each, one is $().each and the other is $.each. The difference is that the former is a built-in function of the jquery object and the latter is a traversal function of the object. It is generally used to obtain different objects in ajax. Data traversal takes json as an example. jquery's getJSON shortcut method can conveniently obtain the json file in the specified URL. jquery will built-in call the js native eval function to parse the json text and convert it into a js object, and then traverse through the each global function to obtain it. The value syntax is each(data,[params],function(current item index, current item)). This is also a big difference from the built-in function each. The index in the built-in function is an identifier used to indicate the position from which Start traversing, followed by the element element to specify how many elements to traverse. The heavy index of each in the global function refers to the key in each key-value pair in json, which is KEY! The author in the jquery basic tutorial gave an example and wrote the corresponding The code however failed to correctly sample the parameters. The sample code is as follows
$.each(data,function(entryIndex,entry){ var html = entry['term']}); Friends who have read this book must be confused about what entryIndex is? In fact, entryIndex is just 'term' However, the author did not use index substitution but filled in the key values directly from json. Through debugging, I found that the following questions are generally translated as indexes. My personal opinion is that the entry should be called the key. It is an attribute value that contains key-value pairs. When a field is imported using the key as an index, the corresponding value is returned through a method similar to the get accessor. I hope it can provide answers to friends who have doubts.

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.

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.


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