Reduce file size for Scala.js

I am looking forward a way to get the benefits of java.time API and reduce the Scala.js-generated file size at same time. I have started evaluating sbt-tzdb v0.1 for that purpose.

I could save averagely 560KB in size (fullOptJS, no gzipped) in my several projects, by removing timezone DB with zonesFilter := { (z:String) => false}. That is 25%～40% savings for my projects. (Note: I suppose my projects require no timezone DB, since my code base uses only OffsetDateTime, LocalDate and Duration right now)

I also investigated why some project can save 40%, but other can save only 25%. My observation shows that my projects can save additional 747KB averagely, if DateTimeFormatter usage is eliminated completely. I suppose that there are huge amounts of locales for DateTimeFormatter as similar as timezone DB.

So… it would be great if one can filter locales for DateTimeFormatter in common with timezone DB. (Sorry in advance, in case of my assumption regarding DateTimeFormatter is incorrect)

The below is my observation of file size reduction in my projects.

Project	Total (KB)	Rest of code (KB)	TimeZoneDB (KB)	DateTimeFormatter (KB)
A	2465	1153	560	752
B	2286	978	560	748
C	2246	939	560	747
D	2237	930	560	747
E	2166	862	560	744
F	2140	835	560	745
G	2130	825	560	745
H	2113	808	560	745
I	2105	801	559	745
J	2083	779	559	745
K	1311	753	557	0
L	1307	749	557	0
M	1283	725	557	0
N	1271	713	557	0

• Total = Rest of code + TimeZoneDB + DateTimeFormatter

The below chart illustrates the above table

[cquiroz]

scalajs-java-locales implemented locales filtering via sbt-locales. I’ll keep this open though as an umbrella for the topic of size reduction

[cquiroz]

That is a great insight, perhaps it could be added to the documentation?