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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4.1
プロミス
79
});
}
};
この関数は、コールバックベースの関数
callbackBasedApi
を受け取って、プロミス化された関数
promisified()
を返します。詳しく見てみましょう。
❶
promisified()
はコンストラクタを使ってプロミスオブジェクトを生成し、即座に呼び出し元
へ戻り値として返している
❷
promisified()
に渡された引数列の末尾に、特別なコールバック関数を追加している。
Node
ではコールバックは必ず末尾の引数となるので、この引数列で
callbackBasedApi()
を呼び出
すことで、追加した関数に処理結果が通知される
❸
callbackBasedApi()
のコールバックがエラーを返した場合、即座にプロミスを
reject
してい
る
❹
callbackBasedApi()
のコールバックが非エラーを返した場合、
2
番目の引数とともにプロミス
を
res
olve
している。
3
番目以降の引数が存在する場合、それらをすべてひとつの配列にまとめて、
その配列とともにプロミスを
resolve
している
❺
作成した引数列で
callbackBasedApi()
を呼び出している
多くのラ イ ブ ラリが、プ ロ ミ ス化のた め の
API
を提供し て い ます。たと え ば、
Q
の
Q.denodeify()
、
Bluebird
の
Promise.promisify()
、
When.js
の
node.lift()
な
どがあります。
4.1.4
逐次処理
理論的な話をしましたので今度は実践です ...
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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.