ExtJS drop-down multiple selection box lovcombo_javascript skills
At first I thought it was very simple, just add an input checkbox to the option. Unexpectedly, it doesn't work. I searched for some implementation methods on the Internet, mainly using div layers to simulate drop-down. I wanted to follow this idea and write one myself based on the specific application of this project, but found that it was too troublesome. I just happened to be using extjs in another project, and found an extension lovcombo, and studied its own examples (with version 2.3 of extjs, version 3.x seems to have problems). The example is not difficult, the key is to add it to the existing code and change the original code as little as possible.
During the use of drop-down multi-select boxes, a lot of logic is mainly focused on the configuration of the data source store and the processing of select events. The data and UI separation model of extjs itself makes the implementation of cascade very easy. Just update the store of the city drop-down box in the select event of the province drop-down box. A small thing to note is that when an option is selected, the value of checkField needs to be used to determine whether the option is selected or canceled. There are also options for selecting all, deselecting all (the two lovcombos have their own methods selectAll and deselectAll) and the number of selected options (you need to traverse the store and detect the checkField value of each item).
//Select event of drop-down box
select:function(combo, record, index)
{
//Selected
if(record.get(this.checkField))
{
//Processing logic when selected
}
else
{
//Unchecked
}
}

JavaScript originated in 1995 and was created by Brandon Ike, and realized the language into C. 1.C language provides high performance and system-level programming capabilities for JavaScript. 2. JavaScript's memory management and performance optimization rely on C language. 3. The cross-platform feature of C language helps JavaScript run efficiently on different operating systems.

JavaScript runs in browsers and Node.js environments and relies on the JavaScript engine to parse and execute code. 1) Generate abstract syntax tree (AST) in the parsing stage; 2) convert AST into bytecode or machine code in the compilation stage; 3) execute the compiled code in the execution stage.

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.


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