


Recently, I am developing a local O2O book rental project, using ASP.NET MVC technology. On the book details page, users can enter the borrowed quantity. JS is used here to control the increase, decrease and verification of the quantity.
1. The quantity must be a number
2. When clicking the increase or decrease button, it must be able to automatically increase or decrease by 1
3. If the content entered by the user is non-numeric, it cannot be entered (except the backspace key)
4. The minimum value entered by the user is 1
5. When the input box leaves the focus, check the value range to ensure that the input box must be a number within the range
Basically the above points
The effect is as follows:
The following is the Html code
<div class="bookNum"> <a id="sub" href="javascript:void(0);">-</a> <input type="text" value="1" id="bookNum"> <a id="add" href="javascript:void(0);">+</a> <a href="javascript:void(0);" id="addCart">加入借阅台</a> <div class="clear"></div> </div>
Look at the first item first:
The input must be numbers
It is easy to think of using keyup event monitoring and replacing non-numeric characters with regular expressions
$("#bookNum").keyup(function(){ var regex = /[^\d]*/g; var numVal = $(this).val(); numVal = numVal.replace(regex,""); numVal = parseInt(numVal)||; numVal = numVal < ? : numVal; $(this).val(numVal); });
In this way, we can ensure that the user input must be a number, and we have done verification. If the value is NaN after converting to an integer using parseInt, let the value be 1. However, we will find a phenomenon that if the user When I want to clear the value inside and enter 20, I find that the value inside always changes to 1
This is unreasonable and the experience is not good. When entering non-digits, that character will be displayed first and then replaced.
Look at websites such as Dangdang and JD.com. When entering non-numbers, there will be no movement at all in the input box. After backspace, you can enter numbers at will. After research, it was found that they used the method of monitoring the keyboard to intercept input.
After improvements:
$("#bookNum").keypress(function(b) { var keyCode = b.keyCode ? b.keyCode : b.charCode; if (keyCode != 0 && (keyCode < 48 || keyCode > 57) && keyCode != 8 && keyCode != 37 && keyCode != 39) { return false; } else { return true; } })
In this way, we ensure that when the user cancels Enter (0), Backspace (8), left and right arrows (37 39) and numbers, they can input normally, and all other keys will be invalid. This will ensure that the input content is a number.
But there is another problem. After the user uses the backspace key to clear the content, the value is empty when the user does not enter anything
This needs to be compensated by using keyup and blur events
$("#bookNum").keypress(function(b) { var keyCode = b.keyCode ? b.keyCode : b.charCode; if (keyCode != 0 && (keyCode < 48 || keyCode > 57) && keyCode != 8 && keyCode != 37 && keyCode != 39) { return false; } else { return true; } }).keyup(function(e) { var keyCode = e.keyCode ? e.keyCode : e.charCode; console.log(keyCode); if (keyCode != 8) { var numVal = parseInt($("#bookNum").val()) || 0; numVal = numVal < 1 ? 1 : numVal; $("#bookNum").val(numVal); } }).blur(function() { var numVal = parseInt($("#bookNum").val()) || 0; numVal = numVal < 1 ? 1 : numVal; $("#bookNum").val(numVal); });
This will ensure verification when users enter numbers.
It’s even easier with button controls:
//增加 $("#add").click(function() { var num = parseInt($("#bookNum").val()) || 0; $("#bookNum").val(num + 1); }); //减去 $("#sub").click(function() { var num = parseInt($("#bookNum").val()) || 0; num = num - 1; num = num < 1 ? 1 : num; $("#bookNum").val(num); });
Okay, this perfectly solves the problem of user input.
Of course, this only explains the js control, other controls can also be added, such as maximum limit, inventory query, server verification, etc. I won’t go into details here.

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.

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.


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

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.

SecLists
SecLists is the ultimate security tester's companion. It is a collection of various types of lists that are frequently used during security assessments, all in one place. SecLists helps make security testing more efficient and productive by conveniently providing all the lists a security tester might need. List types include usernames, passwords, URLs, fuzzing payloads, sensitive data patterns, web shells, and more. The tester can simply pull this repository onto a new test machine and he will have access to every type of list he needs.

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),

SublimeText3 Chinese version
Chinese version, very easy to use

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.