


I am a novice and a fresh graduate. I have never used jquery before. I recently used jquery in a project. In the process of doing it, I took many detours and kept searching. Some usages are summarized for your reference:
The most basic selector syntax includes: id, class, label, attribute, which is consistent with css selector.
The ID selector should add # before the ID. For example, if you want to select a div element with the ID myDivID (
$("#myDivID");
D cannot be repeated, so the ID selector selects a jquery object.
The class selector should add a dot (.) before class. For example, if you want to select an input element with class myInputClass (), you can write like this:
$(".myInputClass");
class can be repeated, so the class selector can select one type of elements, that is, multiple elements, so jquery selects an array, and you can select each element by referring to the subscript: for example
for(var i = 0; i
This way you can iterate out each element.
The tag selector can directly write the tag type. For example, if you want to select a paragraph p tag (), you can write like this:
$("p");
The tag selector is also selected An array, select all p tag elements, you can also use the above method to iterate out all elements.
Attribute selectors should be preceded by square brackets ([]). For example, if you want to select elements with name="xxName", you can write like this:
$("[xxName]");
Select in this way, and the result will be the same An array because name can be repeated.
The ID selector can accurately select an element, but in development we may have to select a group of elements more. How can we accurately select the elements we want? In fact, there are several Selectors can be mixed:
< ;/span>
> ;
p>

For example, we want to select an even number of text labels, that is: a text box that says even. We can choose like this:
First select this div, then select p, then select the text box with type="text", and finally select the even number of positions:
$("#attrValueTab p input[type='text']:even");
Combination selection is very useful in development. You can use the following method to select a checked button or checkbox element:
$("input[name='avDefValue_input']:checked");

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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