通译自：6 Major Features of Node.js 19. Details of Node.js 19 new features… | by Jennifer Fu | Oct, 2022 | Better Programming
【资料图】
Node.js 14 将在 2023 年 4 月结束更新维护，Node.js 16 (LTS) 预计将在 2023 年 9 月结束更新维护。
而Node 19 在 2022-10-18 发布。【相关教程推荐：nodejs视频教程】
我们知道 Node.js 版本分两种：LTS 和 Current
其中，Current 版本通常每 6 个月发布一次。
每年 4 月份发布新的偶数版本；
每年 10 月份发布新的奇数版本；
在刚过去的 10 月，发布的 V19.0.1 成为最新的 “Current” 尝鲜版，它一共带来 6 大特性。
Node.js v19 设置 keepAlive 默认值为 true，这意味着所有出站的 HTTP(s) 连接都将使用 HTTP 1.1 keepAlive，默认时间为 5S；
代码测试：
const http = require("node:http");console.log(http.globalAgent);const https = require("node:https");console.log(https.globalAgent);我们可以对比看看 v16 和 v19 的 node server Agent 配置差异：
V16% nvm use 16Now using node v16.0.0 (npm v7.10.0)% node serverAgent { _events: [Object: null prototype] { free: [Function (anonymous)], newListener: [Function: maybeEnableKeylog] }, _eventsCount: 2, _maxListeners: undefined, defaultPort: 80, protocol: "http:", options: [Object: null prototype] { path: null }, requests: [Object: null prototype] {}, sockets: [Object: null prototype] {}, freeSockets: [Object: null prototype] {}, keepAliveMsecs: 1000, keepAlive : false, maxSockets: Infinity, maxFreeSockets: 256, scheduling: "lifo", maxTotalSockets: Infinity, totalSocketCount: 0, [Symbol(kCapture)]: false}Agent { _events: [Object: null prototype] { free: [Function (anonymous)], newListener: [Function: maybeEnableKeylog] }, _eventsCount: 2, _maxListeners: undefined, defaultPort: 443, protocol: "https:", options: [Object: null prototype] { path: null }, requests: [Object: null prototype] {}, sockets: [Object: null prototype] {}, freeSockets: [Object: null prototype] {}, keepAliveMsecs: 1000, keepAlive: false, maxSockets: Infinity, maxFreeSockets: 256, scheduling: "lifo", maxTotalSockets: Infinity, totalSocketCount: 0, maxCachedSessions: 100, _sessionCache: { map: {}, list: [] }, [Symbol(kCapture)]: false}第 18、40 行，keepAlive 默认设置为 false；
V19% nvm use 19Now using node v19.0.0 (npm v8.19.2)% node serverAgent { _events: [Object: null prototype] { free: [Function (anonymous)], newListener: [Function: maybeEnableKeylog] }, _eventsCount: 2, _maxListeners: undefined, defaultPort: 80, protocol: "http:", options: [Object: null prototype] { keepAlive: true, scheduling: "lifo", timeout: 5000, noDelay: true, path: null }, requests: [Object: null prototype] {}, sockets: [Object: null prototype] {}, freeSockets: [Object: null prototype] {}, keepAliveMsecs: 1000, keepAlive: true, maxSockets: Infinity, maxFreeSockets: 256, scheduling: "lifo", maxTotalSockets: Infinity, totalSocketCount: 0, [Symbol(kCapture)]: false}Agent { _events: [Object: null prototype] { free: [Function (anonymous)], newListener: [Function: maybeEnableKeylog] }, _eventsCount: 2, _maxListeners: undefined, defaultPort: 443, protocol: "https:", options: [Object: null prototype] { keepAlive: true, scheduling: "lifo", timeout: 5000, noDelay: true, path: null }, requests: [Object: null prototype] {}, sockets: [Object: null prototype] {}, freeSockets: [Object: null prototype] {}, keepAliveMsecs: 1000, keepAlive: true, maxSockets: Infinity, maxFreeSockets: 256, scheduling: "lifo", maxTotalSockets: Infinity, totalSocketCount: 0, maxCachedSessions: 100, _sessionCache: { map: {}, list: [] }, [Symbol(kCapture)]: false}第 14、16、42、44 行设置 keepAlive 默认值及时间；
启用 keepAlive 能使连接重用，提高网络的吞吐量。
另外，服务器将在调用 close()自动断开空闲的客户端，内部依靠 http(s).Server.closeAPI 实现；
这些修改，进一步优化了体验和性能。
WebCrypto API 是一个使用密码学构建的系统接口，在 node.js v19 趋于稳定（除 Ed25519、Ed448、X25519、X448 外）。
我们可以通过调用 globalThis.crypto或 require("node:crypto").webcrypto来访问，下面以 subtle加密函数为例；
const { subtle } = globalThis.crypto;(async function() { const key = await subtle.generateKey({ name: "HMAC", hash: "SHA-256", length: 256 }, true, ["sign", "verify"]); console.log("key =", key); const enc = new TextEncoder(); const message = enc.encode("I love cupcakes"); console.log("message =", message); const digest = await subtle.sign({ name: "HMAC" }, key, message); console.log("digest =", digest);})();首先生成 HMAC 密钥，生成的密钥可同时用于验证消息数据完整性和真实性；
然后，对字符串 I love cupcakes加密；
最后创建 消息摘要，它是一种加密散列函数；
在控制台显示：key 、message 、digest 信息
% node serverkey = CryptoKey { type: "secret", extractable: true, algorithm: { name: "HMAC", length: 256, hash: [Object] }, usages: [ "sign", "verify" ]}message = Uint8Array(15) [ 73, 32, 108, 111, 118, 101, 32, 99, 117, 112, 99, 97, 107, 101, 115]digest = ArrayBuffer { [Uint8Contents]: <30 01 7a 5c d9 e2 82 55 6b 55 90 4f 1d de 36 d7 89 dd fb fb 1a 9e a0 cc 5d d8 49 13 38 2f d1 bc>, byteLength: 32}Node.js 已经删除 --experimental-specifier-resolution ，其功能现在可以通过自定义加载器实现。
可以在这个库中测试：nodejs/loaders-test: Examples demonstrating the Node.js ECMAScript Modules Loaders API
git clone https://github.com/nodejs/loaders-test.git% cd loaders-test/commonjs-extension-resolution-loader% yarn install
比如 loaders-test/commonjs-extension-resolution-loader/test/basic-fixtures/index.js 文件：
import { version } from "process";import { valueInFile } from "./file";import { valueInFolderIndex } from "./folder";console.log(valueInFile);console.log(valueInFolderIndex);./file如果没有自定义加载器，不会去查找文件的扩展名，比如 ./file.js或 ./file.mjs
设置自定义加载器后，则可解决上述问题：
import { isBuiltin } from "node:module";import { dirname } from "node:path";import { cwd } from "node:process";import { fileURLToPath, pathToFileURL } from "node:url";import { promisify } from "node:util";import resolveCallback from "resolve/async.js";const resolveAsync = promisify(resolveCallback);const baseURL = pathToFileURL(cwd() + "/").href;export async function resolve(specifier, context, next) { const { parentURL = baseURL } = context; if (isBuiltin(specifier)) { return next(specifier, context); } // `resolveAsync` works with paths, not URLs if (specifier.startsWith("file://")) { specifier = fileURLToPath(specifier); } const parentPath = fileURLToPath(parentURL); let url; try { const resolution = await resolveAsync(specifier, { basedir: dirname(parentPath), // For whatever reason, --experimental-specifier-resolution=node doesn"t search for .mjs extensions // but it does search for index.mjs files within directories extensions: [".js", ".json", ".node", ".mjs"], }); url = pathToFileURL(resolution).href; } catch (error) { if (error.code === "MODULE_NOT_FOUND") { // Match Node"s error code error.code = "ERR_MODULE_NOT_FOUND"; } throw error; } return next(url, context);}测试命令：
% node --loader=./loader.js test/basic-fixtures/index (node:56149) ExperimentalWarning: Custom ESM Loaders is an experimental feature. This feature could change at any time(Use `node --trace-warnings ...` to show where the warning was created)hello from file.js
将不会再报错，正常运行。
在 Node.js v19中，移除了对 DTrace/SystemTap/ETW 的支持，主要是因为资源的优先级问题。
数据表明很少人用到 DTrace、SystemTap 或 ETW，维护它们没有多大的意义。
如果你想恢复使用，可提 issues => github.com/nodejs/node…
Node.js v19 将 V8 JavaScript 引擎更新至 V8 10.7，其中包含一个新函数 Intl.NumberFormat，用于格式化敏感数字。
Intl.NumberFormat(locales, options)
对于不同的语言，传入不同的 locales：
const number = 123456.789;console.log(new Intl.NumberFormat("de-DE", { style: "currency", currency: "EUR" }).format(number));console.log(new Intl.NumberFormat("ja-JP", { style: "currency", currency: "JPY" }).format(number));console.log(new Intl.NumberFormat("ar-SA", { style: "currency", currency: "EGP" }).format(number));console.log(new Intl.NumberFormat("zh-CN", { style: "currency", currency: "CNY" }).format(number));运行时增加了 node --watch 选项。
在 "watch" 模式下运行，当导入的文件被改变时，会重新启动进程。
比如：
const express = require("express");const path = require("path");const app = express();app.use(express.static(path.join(__dirname, "../build")));app.listen(8080, () => console.log("Express server is running on localhost:8080"));% node --watch server(node:67643) ExperimentalWarning: Watch mode is an experimental feature. This feature could change at any time(Use `node --trace-warnings ...` to show where the warning was created)Express server is running on localhost:8080
Node.js 14 将在 2023 年 4 月结束更新维护，Node.js 16 (LTS) 预计将在 2023 年 9 月结束更新维护。
建议大家开始计划将版本按需升级到 Node.js 16（LTS）或 Node.js 18（LTS）。
更多node相关知识，请访问：nodejs 教程！
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