Node.js 19正式發布，聊聊它的 6 大功能！

Node 19已正式發布，以下這篇文章就來帶大家詳解了解Node.js 19的 6 大特性，希望對大家有幫助！

通譯自：6 Major Features of Node.js 19. Details of Node.js 19 new features… | by Jennifer Fu | Oct, 2022 | Better Programming

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Node.js 14 將在2023 年4 月結束更新維護，Node.js 16 (LTS) 預計將在2023 年9 月結束更新維護。

而Node 19 在 2022-10-18 發布。 【相關教學推薦：nodejs影片教學】

我們知道Node.js 版本分成兩種：LTS 和Current

##其中，Current 版本通常每6 個月發布一次。

每年4 月發布新的偶數版本；

每年10 月發布新的奇數版本；

在剛過去的10 月，發布的V19.0.1 成為最新的「Current」 嚐鮮版，它一共帶來6 大功能。

1. HTTP(S)/1.1 KeepAlive 預設為true

Node.js v19 設定keepAlive 預設值為true，這表示所有出站的HTTP( s) 連線都會使用HTTP 1.1 keepAlive，預設時間為5S；

程式碼測試：

const http = require('node:http');
console.log(http.globalAgent);
const https = require('node:https');
console.log(https.globalAgent);

我們可以比較看看v16 和v19 的node server Agent 設定差異：

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 預設為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 行設定keepAlive 預設值及時間；

啟用keepAlive 能使連線重複使用，提高網路的吞吐量。

另外，伺服器將在呼叫

close() 自動斷開空閒的客戶端，內部依賴http(s).Server.close API 實作；

這些修改，進一步優化了體驗和效能。

2. 穩定的WebCrypto API

WebCrypto API 是一個使用密碼學建構的系統接口，在node.js v19 趨於穩定（除Ed25519、Ed448、 X25519、X448 外）。

我們可以透過呼叫

globalThis.crypto 或require('node:crypto').webcrypto 來訪問，下面以subtle 加密函數為例；

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);

})();

首先產生HMAC 金鑰，產生的金鑰可同時用於驗證訊息資料完整性和真實性；

然後，對字串

I love cupcakes 加密；

最後建立訊息摘要，它是一種加密雜湊函數；

在控制台顯示：key 、message 、digest 訊息

% 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. 自訂ESM resolution 調整

Node.js 已經刪除

--experimental-specifier-resolution ，其功能現在可以透過自訂載入器實作。

可以在這個函式庫中測試：

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

例如

loaders-test/ commonjs-extension-resolution-loader/test/basic-fixtures/index.js 檔案：

import { version } from 'process';

import { valueInFile } from './file';
import { valueInFolderIndex } from './folder';

console.log(valueInFile);
console.log(valueInFolderIndex);

./file 如果沒有自訂載入器，就不會去找文件的副檔名，例如./file.js 或./file.mjs

設定自訂載入器後，則可解決上述問題：

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);
}

測試指令：

% 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

將不會再報錯，正常運作。

4. 移除對DTrace/SystemTap/ETW 支援

在Node.js v19中，移除了對DTrace/SystemTap/ETW 的支持，主要是因為資源的優先順序問題。

資料顯示很少人用到 DTrace、SystemTap 或 ETW，維護它們沒有多大的意義。

如果你想恢復使用，可提issues =>

github.com/nodejs/node…

5. 升級V8 引擎至10.7

Node.js v19 將V8 JavaScript 引擎更新至V8 10.7，其中包含一個新函數Intl.NumberFormat，用於格式化敏感數字。

Intl.NumberFormat(locales, options)

對於不同的語言，傳入不同的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. 試驗Node watch 模式

運行時增加了node -- watch 選項。

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

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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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