Allow symbol event names

[stroncium]

Fixes #16

In typescript, complete typing is blocked by microsoft/TypeScript#1863 at the moment, so we relax typing a bit. This relaxation affects defining EventDataMap with number indexes, so Emittery.Typed<{123: string}, 'someevent'> causes no compile time error. However, using any such event will still cause compile time error.

🦄

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Referenced issues

This pull request has been submitted to:

• #16: Support Symbol as eventName

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[stroncium]

@sindresorhus Lemme know if we want this temporal type relaxation or if we will wait for the typescript patch to land so I could update docs accordingly.

[sindresorhus]

Lemme know if we want this temporal type relaxation or if we will wait for the typescript patch to land so I could update docs accordingly.

Doesn't look like the TypeScript project will fix this anytime soon, so let's do it this way.

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Don't forget to update the docs.

[sindresorhus]

@stroncium When this is merged, what do you think of dropping .onAny() and .offAny() later on? Since it can now be represented as:

emitter.on(Emittery.anyEvent, listener);

Would be nice to reduce the API surface.

[stroncium]

@sindresorhus I'd vote against it.
With such change we would basically take 2 different code paths and hide them behind single name(introducing additional eq check, so less performance in theory, though I imagine it would be almost unnoticeable), while also introducing additional symbol with highly specific behavior unlike any other symbol. I'm generally against creating such artificial exceptional behavior, and prefer 2 methods(+counterparts) each doing their own thing instead of one(+counterpart) with a special case, as both API docs are clearer and code using them is easier to read.

[stroncium]

@sindresorhus Docs didn't mention that what event names are supposed to be anywhere(except type in ts), but I think symbol events are really good and must be used as much as possible, so I took freedom to add a couple lines to example and add notification at the beginning of API docs in readme.md.

[sindresorhus]

Could use a better example. This doesn't really show how Symbols can be useful as event names.

[sindresorhus]

Can you add this example to the TS file too?

[stroncium]

We don't have generic usage example in typescript, only examples to clarify some non-obvious things.

[sindresorhus]

@Richienb Can you help review?

[Richienb]

@stroncium Ping!