Microsoft today announced the release of TypeScript 4.0 Beta with several new features and improvements. TypeScript 4.0 is not a major release that comes with larger breaking changes. Instead it is just the natural continuation from TypeScript 3.9. This beta release includes features such as sophisticated slicing and dicing on Tuples, safer exception handling, new operators, control-flow on class properties, faster initial editor startup and more.

What’s new in TypeScript 4.0 beta:

• Variadic Tuple Types
• Labeled Tuple Elements
• Class Property Inference from Constructors
• Short-Circuiting Assignment Operators
• unknown on catch Clauses
• Custom JSX Factories
• Speed Improvements in build mode with --noEmitOnError
• --incremental with --noEmit
• Editor Improvements
  • /** @deprecated */ Support
  • Partial Editing Mode at Startup
  • Smarter Auto-Imports
• Breaking Changes

You can learn more about the above TypeScript features from the source link below.

Source: Microsoft