Node 19 在 2022-10-18 发布。
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。
1. HTTP(S)/1.1 KeepAlive 默认为 true
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 16 Now using node v16.0.0 (npm v7.10.0) % node server Agent { _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 19 Now using node v19.0.0 (npm v8.19.2) % node server Agent { _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.close API 实现；
这些修改，进一步优化了体验和性能。
2. 稳定的 WebCrypto API
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 server key = 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 }
3. 自定义 ESM resolution 调整
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。
4. 移除对 DTrace/SystemTap/ETW 支持
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…
5. 升级 V8 引擎至 10.7
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));
6. 试验 Node watch 模式
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）。
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