TypeScript 4.0
https://www.typescriptlang.org/docs/handbook/release-notes/typescript-4-0.html
Variadic Tuple Types
結構でかい
Labeled Tuple Elements
Class Property Inference from Constructors
noImplicitAny
assignmeng assertion
Short-Circuiting Assignment Operators
unknown on catch Clause Bindings
Custom JSX Factories
Speed Improvements in build mode with --noEmitOnError
--incremental with --noEmit
Editor Improvements