Promise patterns

Promises are great for giving us a way of writing asynchronous code without having to indent our code but if that's the only thing you're using them for then you're missing the point of promises. Promises are an abstraction that make doing several things easier. They have two properties that make them easier to work with: You can attach more than one callback to a single promise values and states

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Promise/A+の拡張例としてコールバック関数をPromiseに変換することについてやエラーハンドリング、複数のpromiseが全て解決した時に次を呼ぶような仕組みの実装などについて。