JavaScript 示例详解(经典收藏)
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JavaScript,作为全球最广泛使用的编程语言之一,是创建交互式网页和动态应用的关键工具。这份“JavaScript 示例详解(经典收藏)”包含了一系列精选的代码示例,旨在帮助开发者深入理解和熟练掌握JavaScript的核心概念与实际应用。 一、变量与数据类型 在JavaScript中,变量是存储值的容器,通过`var`, `let`, 或 `const` 关键字声明。JavaScript有七种数据类型:Undefined、Null、Boolean、Number、BigInt、String 和 Symbol。例如: ```javascript let num = 42; // Number 类型 let str = "Hello"; // String 类型 let bool = true; // Boolean 类型 let obj = {}; // Object 类型 ``` 二、控制结构 1. 条件语句:`if...else` 用于根据条件执行不同的代码块。 ```javascript if (num > 0) { console.log("Positive number"); } else { console.log("Non-positive number"); } ``` 2. 循环:`for`、`while` 和 `do...while` 用于重复执行代码。 ```javascript for (let i = 0; i < 5; i++) { console.log(i); } ``` 三、函数 函数是一组可重用的代码,可以通过调用其名称来执行。可以有参数和返回值。 ```javascript function greet(name) { return "Hello, " + name; } console.log(greet("Alice")); // 输出 "Hello, Alice" ``` 四、对象与数组 1. 对象:键值对的集合,用大括号 `{}` 包裹。 ```javascript let person = { name: "John Doe", age: 30, }; ``` 2. 数组:有序元素列表,用方括号 `[]` 包裹。 ```javascript let fruits = ["apple", "banana", "orange"]; ``` 五、数组方法与对象操作 1. 数组方法:如 `push`, `pop`, `slice`, `splice`, `map`, `filter` 等。 ```javascript fruits.push("grape"); // 添加元素到数组末尾 ``` 2. 对象操作:`Object.keys()`, `Object.values()`, `Object.assign()` 等。 ```javascript let keys = Object.keys(person); // 获取对象的键数组 ``` 六、作用域与闭包 1. 全局与局部作用域:`var` 声明的变量在整个脚本或函数中可见,`let` 和 `const` 在块级作用域内。 2. 闭包:函数能访问并操作其外部作用域的变量,即使在其外部执行。 七、事件与DOM操作 JavaScript 可以响应用户交互,如点击按钮,以及操作文档对象模型(DOM)来改变网页内容。 ```javascript document.getElementById("myButton").addEventListener("click", function() { alert("Button clicked!"); }); ``` 八、异步编程 1. 回调函数:处理异步操作,如网络请求。 ```javascript fetch("https://api.example.com/data") .then(response => response.json()) .then(data => console.log(data)); ``` 2. Promise:更优雅的异步处理方式。 3. async/await:Promise 的语法糖,使得异步代码可读性更强。 九、ES6新特性 包括类(Class)、箭头函数(Arrow Function)、模板字符串(Template Literal)、解构赋值(Destructuring)、模块导入导出(Module)、默认参数(Default Parameters)等。 以上只是JavaScript基础知识的冰山一角,这个“JavaScript 示例详解(经典收藏)”可能包含了更多高级主题,如面向对象编程、模块化、错误处理、性能优化等方面的内容,每个话题都值得深入研究和实践。通过学习和理解这些示例,开发者可以构建更高效、更健壮的JavaScript应用程序。
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