May 2019
Intermediate to advanced
464 pages
9h 22m
Japanese
Content preview from Node.jsデザインパターン 第2版
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176
6
章 オブジェクト指向デザインパターンの
Node.js
への適用
const fs = fsAdapter(db);
プログラムを再実行すると、同じ出力が得られるはずですが、指定されたファイルはファイルシステ
ムを使って読み書きされてはいないという事実が異なっています。アダプタを使って実行されたすべて
の操作は、
LevelUP
データベース上で実行される操作に置き換えられています。
今作成したアダプタは馬鹿げたものに見えるかもしれません。実際のファイルシステムの代わりに
データベースを使っても、何の役にも立たないのではないかと思われたでしょう。しかし、
LevelUP
自
体のアダプタにブラウザでもデータベースを実行できるようにするものがあることを思い出してくださ
い。そのようなアダプタのひとつが
level.js
（
https://npmjs.org/package/level-js
）です。これでア
ダプタのもつ意味が明らかになりました。モジュール
fs
を利用するブラウザのコードと共用できるの
です。たとえば
3
章で作成したウェブスパイダーは、動作中にダウンロードしたウェブページを保存す
るのに
fs
API
を使っています。今作成したアダプタに少し手を入れれば、ウェブスパイダーがブラウ
ザ内で実行できるのです。この先、ブラウザとコードを共用したい場合にアダプタがきわめて重要なパ
ターンであることがわかってきます。
8
章でさらに詳しく見ていきます。
6.5.2
実践での利用
アダプタパターンには実践での応用例が多数あ ...
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.