An expression is a phrase in JavaScript, and the JavaScript interpreter will evaluate it to produce a result. Constants, variable names, array access, etc. in the program are all expressions. The most common way to combine simple expressions into complex expressions is to use operators. The original expression is the simplest expression. "Primary expression". Is the smallest unit of expression ———— No other expressions are included. Constants, literals, keywords, and variables are all primitive expressions
1.23 "hello" /pattern/ true false null this i sum undefined
Initialization expressions for objects and arrays
Initialization expressions for objects and arrays are actually a newly created object and array. These expressions are sometimes called Make "object literals" and "array literals"!
[] [1+2, 3+4] var sparseArray = [1,,,,,5] // 数组分割逗号之前的元素可以省略,空位默认填充 undefined var matrix = [[1,2,3], [4,5,6], [7,8,9]] var p = { x: 2.3, y: -1.2} var q = {} q.x = 2.3; q.y = -1.3
Function definition expression
var square = function(x) { return x*x }
Property access expression
// expression.identifier // expression[expression] var o = { x:1, y:{z:3} }; var a = [0, 4, [5, 6]]; o.x // => 1 表达式 o 的 x 属性 o.y.z // => 3 表达式 o.y 的属性 z o["x"] // => 1 对象 o 的 x 属性 a[1] // => 4 表达式 a 中索引为 1 的元素 a[2]["1"] // => 6 表达式 a[2] 中索引为 1 的元素 a[0].x // => 1 表达式 a[0] 的 x 属性 /*不管使用哪种形式的属性访问表达式,在「.」和「[」 之前的表达式总是会首先计算。如果计算结果是 null 或者 undefined,表达式会抛出一个类型错误异常,因为这两个值都不能包含任意属性。如果运算结果不是对象(或者数组),JavaScript 会将其转换为对象。如果对象表达式后跟随一对方括号,则会计算方括号内的表达式的值并将它转换为字符串,不论哪种情况,如果命名的属性不存在,那么整个属性访问表达式的值就是 undefined */

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.


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