JavaScript基础入门:从变量到语法详解

需积分: 0 16 下载量 74 浏览量 更新于2024-09-08 收藏 1.18MB PDF 举报
JavaScript,全称为JavaScript Programming Language,是一种广泛应用于网页开发的脚本语言。它由网景公司开发,旨在增强网页的交互性和动态表现力。作为一门基于浏览器的语言,JavaScript在HTML文档中执行,无需预先编译,具有以下关键特点: 1. **静态与动态特性**: JavaScript是静态类型的脚本语言,这意味着它在运行时检查数据类型,而非编译时。这种设计使得JavaScript更加灵活,适应性强,但可能会影响性能。 2. **面向对象编程**: JavaScript是基于对象的语言,所有的事物(包括函数、数组等)都可以视为对象。这允许开发者使用封装、继承和多态等面向对象编程原则。 3. **事件驱动**: JavaScript的核心工作原理是事件驱动,即当用户与网页交互(如点击、滑动)时,浏览器会触发相应的事件,JavaScript负责响应并执行相应的代码。 4. **应用场景**: - 表单验证:确保用户输入的有效性。 - AJAX(Asynchronous JavaScript and XML):实现异步数据交换,提升用户体验。 - 与服务器交互:处理前后端通信,尤其在现代Web应用中不可或缺。 - 网页特效:动态加载、轮播图等视觉效果。 - 简单游戏:如早期的贪吃蛇游戏。 5. **快速入门**: 对于初学者,可以通过编写简单的脚本来快速熟悉语法和基本概念,例如控制元素显示、响应用户输入等。 6. **与Java的区别**: 尽管名字相似,JavaScript与Java并无直接关联,它们各自属于不同的编程范式。Java是一种编译型语言,而JavaScript是解释型语言,执行效率上有差异。 7. **HTML中的书写方式**: - 嵌入式:直接在HTML `<script>`标签内编写,适用于小型脚本,仅限当前页面。 - 外链式:通过`<script src>`引用外部`.js`文件,可复用且跨页面,更便于代码管理和维护。 8. **注释**: JavaScript支持单行注释(//)和多行注释(/* ... */),帮助开发者理解代码。 9. **变量**: - 变量是存储数据的容器,通过`var`、`let`或`const`关键字声明。 - 命名规则:遵循标识符命名规范,避免使用保留字。 - 赋值操作用于将值与变量关联。 10. **输出方法**: 学习了变量和赋值后,可以使用`console.log()`等方法将数据输出到浏览器控制台,便于调试。 11. **语法和运算符**: JavaScript有丰富的语法结构,包括条件语句、循环、函数等。运算符包括算术运算、比较运算、逻辑运算等。 12. **数据类型**: JavaScript支持多种数据类型,如字符串、数字、布尔、null、undefined、对象和数组等,了解不同数据类型有助于高效地编写代码。 通过这个基础教程,读者可以建立起JavaScript的基本框架,并为进一步深入学习准备。后续章节可能会涉及函数、DOM操作、异步编程、模块化等高级主题。
2018-09-10 上传
JavaScript is no longer to be feared or loathed – the world’s most popular and ubiquitous language has evolved into a respectable language. Whether you’re writing frontend applications or server side code, the phenomenal features from ES6 and beyond – like the rest operator, generators, destructuring, object literals, arrow functions, modern classes, promises, async, and metaprogramming capabilities – will get you excited and eager to program with JavaScript. You’ve found the right book to get started quickly and dive deep into the essence of modern JavaScript. Learn practical tips to apply the elegant parts of the language and the gotchas to avoid. JavaScript is a black swan that no one, including the author of the language, thought would become a popular and ubiquitous language. Not long ago, it was the most hated and feared language you could use to program the web. JavaScript ES6 and beyond has gone through a significant makeover. Troublesome features have been replaced with better, elegant, more reliable alternatives. This book includes many practical examples and exercises to help you learn in depth. It will not bore you with idiosyncrasies and arcane details intended for bad interview questions. Instead, it takes you into key features that you can readily use in your day-to-day projects. Whether you program the frontend or the server side, you can now write concise, elegant, and expressive JavaScript with newer features like default parameters, template literals, rest and spread operators, destructuring, arrow functions, and generators. Take it up a notch with features like infinite series, promises, async, and metaprogramming to create flexible, powerful, and extensible libraries. While the evolved features of the language will draw you in, the hundreds of examples in this book will pin the concepts down, for you to use on your projects. Take command of modern JavaScript and unlock your potential to create powerful applications. What You Need: To try out the examples in the book you will need a computer with Node.js, a text editor, and a browser like Chrome installed in it.