<!DOCTYPE html> <html> <head lang="en"> <meta charset="UTF-8"> <title>js 基础</title> <script type="text/css" src="xxx.js"></script> <!--外链式 --> </head> <body> <p onclick="alert('我是行内式')">你好</p> <script type="text/javascript"> //内嵌式 // 输出语句 alert("我是内嵌式"); prompt("请输入:"); confirm("你好吗?"); console.log("我是控制台输出"); console.error("我是错误");//了解 console.warn("我是警告");//了解 document.write("<h1 id="我是h-标签">我是h1标签</h1>");//页面输出内容而且识别标签 //数据类型 var str1 = "aa"; var str2 = "123"; var num = 123; var bool = true; //true false var kong =null; var wu ; //undefined 未定义 //查看数据类型 (typeof 变量 ) var type = typeof(str1); //类型转换 成数字number var str = "123.2a";//字符串类型的数字 var bool = true; var num1 = parseInt(str); //取第一部分数字 并取整 没有数字Nan 输出:123 var num2 = parseFloat(str); //取第一部分数字 保留小数 输出:123.2 var num3 = Number(str); //有非数字就会报 Nan 没有就全部转换成数字 console.log(typeof Number(bool)); //boolean 转成1 console.log(typeof (str-0)); //数子类型的字符串在处"+"外都会有隐士类型转换 console.log(typeof (bool-0)); console.log(typeof (str*1)); console.log(typeof (bool*1)); console.log(typeof (str/1)); console.log(typeof (bool/1)); console.log(typeof typeof (bool/1)); //数据类型是用string定义的 //类型转换 成字符串String var num4 = 123; var num5 = num+""; //"+"在有字符串在于运算的时候表示拼接 而非相加 var num6 = num.toString(); var num7 = String(num2); console.log(typeof num5); //进制转换 var num8 = parseInt(111,2); //任意进制转换成十进制。111:值,2:进制 输出:7 var num = 10; var renyi = num.toString(16); //十进制转换成任意进制 输出:a //特殊的 undefined 和 null console.log(undefined == null); //true console.log(undefined === null); //false console.log(undefined+10); // Nan 不是一个数字 console.log(null+10); //10 //操作符种类 一,算数运算符(+—*/...) a) 一元运算符:正号,负号,++,--,平方等一个变量就能运算 b) 二元运算符:+-*/%等两个变量才能运算 c) 三元运算符: 值1?值2:值3; 二,逻辑运算符( ||&& ! )(或且非) 三,比较运算符(<,>,==,>=...) 四,赋值运算符(=,+=,-=,*=,/=,%=) //优先级 1 () 2 !,-(负数),++,-- (正数省略+)(一元运算) 3 *,/,% 4 +,- (加,减)(二元运算) 5 <,<=,<,>= (一级逻辑运算) 6 ==,!=,===,!==, (二级逻辑运算) 7 && (三级级逻辑运算) 8 || 9 ?: (三元运算) 10 =,+=,-=,*=,/=,%= (赋值运算) // && 和 || 运算 一 && 链接两个boolean类型,有一个是false结果就是false, A与B 都是true取后面,都是false取前面 二 || 链接两个boolean类型,有一个是true结果就是true, A或B 都是true取前面,都是false取后面 </script> </body> </html>
This article explains the basic data types and conversion base operators of js. For more related content, please pay attention to the PHP Chinese website.
Related recommendations:
The above is the detailed content of js basic data types and conversion base operators. For more information, please follow other related articles on the PHP Chinese website!

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.

I built a functional multi-tenant SaaS application (an EdTech app) with your everyday tech tool and you can do the same. First, what’s a multi-tenant SaaS application? Multi-tenant SaaS applications let you serve multiple customers from a sing

This article demonstrates frontend integration with a backend secured by Permit, building a functional EdTech SaaS application using Next.js. The frontend fetches user permissions to control UI visibility and ensures API requests adhere to role-base

JavaScript is the core language of modern web development and is widely used for its diversity and flexibility. 1) Front-end development: build dynamic web pages and single-page applications through DOM operations and modern frameworks (such as React, Vue.js, Angular). 2) Server-side development: Node.js uses a non-blocking I/O model to handle high concurrency and real-time applications. 3) Mobile and desktop application development: cross-platform development is realized through ReactNative and Electron to improve development efficiency.

The latest trends in JavaScript include the rise of TypeScript, the popularity of modern frameworks and libraries, and the application of WebAssembly. Future prospects cover more powerful type systems, the development of server-side JavaScript, the expansion of artificial intelligence and machine learning, and the potential of IoT and edge computing.

JavaScript is the cornerstone of modern web development, and its main functions include event-driven programming, dynamic content generation and asynchronous programming. 1) Event-driven programming allows web pages to change dynamically according to user operations. 2) Dynamic content generation allows page content to be adjusted according to conditions. 3) Asynchronous programming ensures that the user interface is not blocked. JavaScript is widely used in web interaction, single-page application and server-side development, greatly improving the flexibility of user experience and cross-platform development.


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

AI Hentai Generator
Generate AI Hentai for free.

Hot Article

Hot Tools

SublimeText3 Mac version
God-level code editing software (SublimeText3)

Safe Exam Browser
Safe Exam Browser is a secure browser environment for taking online exams securely. This software turns any computer into a secure workstation. It controls access to any utility and prevents students from using unauthorized resources.

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.

ZendStudio 13.5.1 Mac
Powerful PHP integrated development environment