Optional Parameters in Callbacks
Don’t use optional parameters in callbacks unless you really mean it:
1 2 3 4 | /* WRONG */interface Fetcher { getObject(done: (data: any, elapsedTime?: number) => void): void;} |
This has a very specific meaning: the done callback might be invoked with 1 argument or might be invoked with 2 arguments. The author probably intended to say that the callback might not care about the elapsedTime parameter, but there’s no need to make the parameter optional to accomplish this – it’s always legal to provide a callback that accepts fewer arguments.
Do write callback parameters as non-optional:
1 2 3 4 | /* OK */interface Fetcher { getObject(done: (data: any, elapsedTime: number) => void): void;} |
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