回调中的可选参数

❌ 不要在回调中使用可选参数，除非你真的是这个意思：

❌ Don't use optional parameters in callbacks unless you really mean it:

/* WRONG */
interface Fetcher {
  getObject(done: (data: unknown, elapsedTime?: number) => void): void;
}

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/* OK */
interface Fetcher {
  getObject(done: (data: unknown, elapsedTime: number) => void): void;
}