formatNumberToParts, the engine behind formatNumber, built a new
Intl.NumberFormat on every call. It is invoked for essentially every
numeric state render, and constructing an Intl.NumberFormat is
comparatively expensive.
Cache the formatters in a Map keyed by (locale, options). Unlike the
single-entry memoizeOne used for the date formatters, the number format
options are derived per value, so a multi-entry cache is needed to avoid
thrashing. The number of distinct combinations is small and bounded in
practice. Output is unchanged.
Franck Nijhof
Wendelin