前端面试必刷10大核心考点

前端面试题精选与解析

闭包及其应用场景

闭包是指函数能够访问并记住其词法作用域外的变量，即使函数在其定义的作用域之外执行。常见应用包括模块化开发、私有变量封装和函数柯里化。

function createCounter() {
  let count = 0;
  return function() {
    return ++count;
  };
}
const counter = createCounter();
console.log(counter()); // 1

Promise与异步编程

Promise是处理异步操作的对象，具有三种状态：pending、fulfilled和rejected。async/await是建立在Promise之上的语法糖。

async function fetchData() {
  try {
    const res = await fetch('https://api.example.com/data');
    return await res.json();
  } catch (error) {
    console.error('Fetch failed:', error);
  }
}

虚拟DOM与Diff算法

虚拟DOM是真实DOM的轻量级JavaScript表示，Diff算法通过比较新旧虚拟DOM树的最小差异来高效更新界面。React和Vue均采用此机制优化性能。

CSS盒模型与布局

标准盒模型宽度=content，IE盒模型宽度=content+padding+border。Flex布局通过flex-container和flex-item属性实现弹性排版。

.container {
  display: flex;
  justify-content: space-between;
}
.item {
  flex: 1;
  margin: 0 10px;
}

跨域解决方案

常见跨域处理方法包括CORS（服务端设置Access-Control-Allow-Origin）、JSONP（动态创建script标签）、Nginx反向代理和WebSocket协议。

性能优化策略

关键优化手段：代码分割（Code Splitting）、图片懒加载（Intersection Observer API）、CDN加速、Service Worker缓存和Web Workers处理CPU密集型任务。

前端安全防护

XSS防御：对用户输入进行转义（如DOMPurify库）。CSRF防护：使用SameSite Cookie、验证Referer头和添加Token校验。

TypeScript核心特性

类型系统提供静态类型检查，接口（Interface）定义契约，泛型增强代码复用性，装饰器实现元编程。

interface User {
  name: string;
  id: number;
}
function getUser<T extends User>(user: T): T {
  return user;
}

前端工程化实践

现代工具链包括Webpack/Vite构建工具、Babel转译器、ESLint代码检查、Jest单元测试和Docker容器化部署。

框架设计原理

响应式系统通过Object.defineProperty或Proxy实现数据绑定。单向数据流（如Redux）通过集中式状态管理降低组件耦合度。

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