Deno 的标准库有哪些常用模块？ - 面试题

Deno 的标准库（Standard Library）是一组经过精心设计、测试和维护的模块，为开发者提供了高质量、可复用的代码。标准库涵盖了从文件系统操作到网络编程的各个方面，是 Deno 生态系统的重要组成部分。

标准库概述

Deno 标准库托管在 https://deno.land/std/，所有模块都经过严格的代码审查和测试，确保代码质量和安全性。

版本管理

标准库使用语义化版本控制，建议在导入时指定版本：

typescript
// 推荐：指定版本
import { serve } from "https://deno.land/std@0.208.0/http/server.ts";

// 不推荐：使用最新版本
import { serve } from "https://deno.land/std/http/server.ts";

主要模块

1. HTTP 模块

HTTP 服务器

typescript
import { serve } from "https://deno.land/std@0.208.0/http/server.ts";

const handler = async (req: Request): Promise<Response> => {
  const url = new URL(req.url);
  
  if (url.pathname === "/") {
    return new Response("Hello, Deno!", {
      headers: { "content-type": "text/plain" },
    });
  }
  
  return new Response("Not Found", { status: 404 });
};

await serve(handler, { port: 8000 });

HTTP 客户端

typescript
import { fetch } from "https://deno.land/std@0.208.0/http/fetch.ts";

const response = await fetch("https://api.example.com/data");
const data = await response.json();
console.log(data);

2. 文件系统模块

文件操作

typescript
import { ensureDir, ensureFile } from "https://deno.land/std@0.208.0/fs/mod.ts";

// 确保目录存在
await ensureDir("./data/uploads");

// 确保文件存在
await ensureFile("./config.json");

// 复制文件
import { copy } from "https://deno.land/std@0.208.0/fs/copy.ts";
await copy("source.txt", "destination.txt");

// 移动文件
import { move } from "https://deno.land/std@0.208.0/fs/move.ts";
await move("old.txt", "new.txt");

遍历目录

typescript
import { walk } from "https://deno.land/std@0.208.0/fs/walk.ts";

for await (const entry of walk("./src")) {
  console.log(entry.path);
  if (entry.isFile) {
    console.log(`File: ${entry.name}`);
  } else if (entry.isDirectory) {
    console.log(`Directory: ${entry.name}`);
  }
}

3. 路径模块

typescript
import { join, basename, dirname, extname, resolve } from "https://deno.land/std@0.208.0/path/mod.ts";

const path = "/home/user/documents/file.txt";

console.log(basename(path));  // "file.txt"
console.log(dirname(path));   // "/home/user/documents"
console.log(extname(path));   // ".txt"
console.log(join("/home", "user", "docs"));  // "/home/user/docs"
console.log(resolve("./src", "file.ts"));    // 绝对路径

4. 编码模块

Base64 编码

typescript
import { encodeBase64, decodeBase64 } from "https://deno.land/std@0.208.0/encoding/base64.ts";

const text = "Hello, Deno!";
const encoded = encodeBase64(text);
console.log(encoded);  // "SGVsbG8sIERlbm8h"

const decoded = decodeBase64(encoded);
console.log(decoded);  // "Hello, Deno!"

Hex 编码

typescript
import { encodeHex, decodeHex } from "https://deno.land/std@0.208.0/encoding/hex.ts";

const data = new TextEncoder().encode("Hello");
const hex = encodeHex(data);
console.log(hex);  // "48656c6c6f"

const decoded = decodeHex(hex);
console.log(new TextDecoder().decode(decoded));  // "Hello"

5. 测试模块

typescript
import { assertEquals, assertThrows } from "https://deno.land/std@0.208.0/testing/asserts.ts";

Deno.test("assertEquals example", () => {
  assertEquals(1 + 1, 2);
  assertEquals("hello", "hello");
});

Deno.test("assertThrows example", () => {
  assertThrows(
    () => {
      throw new Error("Test error");
    },
    Error,
    "Test error"
  );
});

6. 日志模块

typescript
import { getLogger, setup, handlers } from "https://deno.land/std@0.208.0/log/mod.ts";

await setup({
  handlers: {
    console: new handlers.ConsoleHandler("INFO"),
  },
  loggers: {
    default: {
      level: "INFO",
      handlers: ["console"],
    },
  },
});

const logger = getLogger();
logger.info("Application started");
logger.warning("This is a warning");
logger.error("An error occurred");

7. UUID 模块

typescript
import { v4 as uuidv4, v5 as uuidv5 } from "https://deno.land/std@0.208.0/uuid/mod.ts";

const id1 = uuidv4();
console.log(id1);  // 生成随机 UUID

const id2 = uuidv5("hello", uuidv4());
console.log(id2);  // 基于命名空间生成 UUID

8. 日期时间模块

typescript
import { format, parse } from "https://deno.land/std@0.208.0/datetime/mod.ts";

const now = new Date();
const formatted = format(now, "yyyy-MM-dd HH:mm:ss");
console.log(formatted);  // "2024-01-15 10:30:45"

const parsed = parse("2024-01-15", "yyyy-MM-dd");
console.log(parsed);  // Date 对象

9. 颜色模块

typescript
import { red, green, blue, bold } from "https://deno.land/std@0.208.0/fmt/colors.ts";

console.log(red("Error message"));
console.log(green("Success message"));
console.log(blue("Info message"));
console.log(bold("Important message"));

10. 异步模块

typescript
import { delay, retry } from "https://deno.land/std@0.208.0/async/mod.ts";

// 延迟执行
await delay(1000);  // 等待 1 秒

// 重试机制
const result = await retry(async () => {
  const response = await fetch("https://api.example.com");
  if (!response.ok) throw new Error("Request failed");
  return response.json();
}, {
  maxAttempts: 3,
  minTimeout: 1000,
});

11. 流模块

typescript
import { copy } from "https://deno.land/std@0.208.0/streams/copy.ts";

const file = await Deno.open("input.txt");
const output = await Deno.open("output.txt", { create: true, write: true });

await copy(file, output);

file.close();
output.close();

12. 命令行模块

typescript
import { parseArgs } from "https://deno.land/std@0.208.0/cli/parse_args.ts";

const args = parseArgs(Deno.args, {
  boolean: ["verbose", "help"],
  string: ["output"],
  default: { verbose: false },
});

console.log(args);
// 运行: deno run script.ts --verbose --output=result.txt
// 输出: { _: [], verbose: true, help: false, output: "result.txt" }

实际应用示例

文件上传服务器

typescript
import { serve } from "https://deno.land/std@0.208.0/http/server.ts";
import { ensureDir } from "https://deno.land/std@0.208.0/fs/mod.ts";
import { extname } from "https://deno.land/std@0.208.0/path/mod.ts";

const UPLOAD_DIR = "./uploads";
await ensureDir(UPLOAD_DIR);

const handler = async (req: Request): Promise<Response> => {
  const url = new URL(req.url);

  if (req.method === "POST" && url.pathname === "/upload") {
    const formData = await req.formData();
    const file = formData.get("file") as File;
    
    if (file) {
      const filename = `${crypto.randomUUID()}${extname(file.name)}`;
      const filepath = `${UPLOAD_DIR}/${filename}`;
      
      const content = await file.arrayBuffer();
      await Deno.writeFile(filepath, new Uint8Array(content));
      
      return new Response(JSON.stringify({ filename }), {
        headers: { "Content-Type": "application/json" },
      });
    }
  }

  return new Response("Not Found", { status: 404 });
};

await serve(handler, { port: 8000 });

日志记录系统

typescript
import { getLogger, setup, handlers, LogRecord } from "https://deno.land/std@0.208.0/log/mod.ts";

class CustomHandler extends handlers.BaseHandler {
  override format(logRecord: LogRecord): string {
    const { levelName, msg, datetime } = logRecord;
    return `[${datetime.toISOString()}] [${levelName}] ${msg}`;
  }
}

await setup({
  handlers: {
    console: new CustomHandler("DEBUG"),
  },
  loggers: {
    default: {
      level: "DEBUG",
      handlers: ["console"],
    },
  },
});

const logger = getLogger();

async function processData(data: any) {
  logger.debug(`Processing data: ${JSON.stringify(data)}`);
  
  try {
    const result = await performOperation(data);
    logger.info("Operation completed successfully");
    return result;
  } catch (error) {
    logger.error(`Operation failed: ${error.message}`);
    throw error;
  }
}

标准库的优势

高质量代码：所有模块都经过严格审查和测试
类型安全：完整的 TypeScript 类型定义
文档完善：详细的 API 文档和示例
定期更新：持续维护和功能增强
一致性：统一的代码风格和 API 设计
安全可靠：经过安全审计，无已知漏洞

最佳实践

指定版本：始终使用特定版本的标准库
优先使用：在可能的情况下优先使用标准库而非第三方库
查看文档：使用 deno doc 查看模块文档
贡献代码：发现问题时可以提交 PR 贡献代码
关注更新：定期查看标准库的更新日志

Deno 标准库为开发者提供了强大而可靠的基础设施，大大简化了常见任务的实现，是 Deno 生态系统的重要支柱。