Set package sideEffects to false

[federicocarboni]

Allows bundlers to tree-shake out the temporal polyfill when it is imported but not used.

If (or when) in the future the polyfill patches the global object "sideEffects" may be changed to an array to declare the side effects of a specific entry (e.g. @js-temporal/polyfill/global has side effects while other entry points do not).

[12wrigja]

There are package-local side-effects when modules are evaluated (example:

temporal-polyfill/lib/timezone.ts

Lines 172 to 174 in 8fd0dea

	MakeIntrinsicClass(TimeZone, 'Temporal.TimeZone');
	DefineIntrinsic('Temporal.TimeZone.prototype.getOffsetNanosecondsFor', TimeZone.prototype.getOffsetNanosecondsFor);
	DefineIntrinsic('Temporal.TimeZone.prototype.getPossibleInstantsFor', TimeZone.prototype.getPossibleInstantsFor);

).

It is possible to convert from one Temporal type to another today using prototype methods which require references to the other module's classes being registered using these side-effects (e.g. toZonedDateTime:

temporal-polyfill/lib/instant.ts

Line 151 in 8fd0dea

return ES.CreateTemporalZonedDateTime(GetSlot(this, EPOCHNANOSECONDS), timeZone, 'iso8601');

). Would this method still work with this sideEffect flag if user code only ever imported Instant (as Instant does not and can not have a direct import on ZonedDateTime)?

[federicocarboni]

sideEffects does not affect function calls. It is a hint to module bundlers that whole modules may be ignored if none of their exports are used.

Just in case, I checked built files and they are bit-by-bit identical with and without sideEffects.

[12wrigja]

Ok - thank you for checking. Seems reasonable to me.