TypeScriptのclass
https://numb86-tech.hatenablog.com/entry/2020/02/21/144155
private propertyの
#hoge
と
private hoge
の違い
https://blog.jxck.io/entries/2019-03-14/private-class-field.html
soft-private
private hoge
型上はerrorになるが、compile後のJSではアクセス可能
hard-private
#hoge
本当のprivate
ECMAScriptにある
https://github.com/tc39/proposal-class-fields
https://qiita.com/suin/items/fafc81be5a7222648863
https://book.yyts.org/features/classes