February 2013
Intermediate to advanced
380 pages
7h 45m
Japanese
Content preview from Nodeクックブック
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151
レシピ 5.3 socket.io 越しにコールバック関数を実行する
server.js
を実行し、
http://localhost:8080
にアクセスすると、ブラウザに以下のようなメッ
セージが表示されます。
4 x 4 is 16
44GT44KM44GM44Gd44Gu5paH56ug44Gn44GZ44CC
を受信しました。
解説
クライアントがサーバに接続すると同時に、サーバとクライアント双方が
emit
メソッドでカス
タムイベントを送出します（カスタムイベントについてはミニレシピ
5.2.1
を参照してください）。
クライアントとサーバの双方で、
emit
の最後のパラメータに関数を渡しています。
emit
の最後
の引数が関数の場合、リモート側で定義されているカスタムイベントのハンドラで
cb
パラメータ
を生成します。
この
cb
パラメータには関数が渡されますが、これは実際の関数ではなく、イベント送信元の
emit
メソッドに引数を送り返すための
socket.io
の内部関数です。
emit
はリモートのイベントリ
スナからこれらの引数を受け取り、ローカル環境で関数を実行します。
それぞれの関数が実行する環境は重要です。もしサーバ側で定義された
give me a sentence
の
コールバック関数がクライアント側で実行されると、クライアント側では
Buffer
オブジェクトを
持たないため、エラーが発生します。もし
give me a number
が
DOM
や
DOM
操作のメソッドを
持たないサーバ側（
Node
）で実行されても同様にエラーが発生します。 ...
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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.