Microsoft has announced the first beta release for TypeScript 4.0. The most recent version of the language, TypeScript 3.9, was released last month

TypeScript 3.9 had introduced speed and user experience improvements. TypeScript 4.0 follows Microsoft’s pattern of trying to introduce new features that don’t introduce breaking changes for older versions. 

The next version doesn’t add many breaking changes, but adds new features such as variadic tuple types, labeled tuple elements, class property inference from constructors, short-circuiting assignment operators, custom JSX factories, and more.  

The few breaking changes that are included in this release are “lib.d.ts” declaration changes, errors when properties try to override accessors, optional operands for “delete”, and deprecation of the node factory. 

“This beta takes us on our first step into TypeScript 4.0, and while it brings a new major version, don’t fret – there are no substantially larger breaking changes than usual. Our philosophy in evolving TypeScript has always been to provide an upgrade path that minimizes disruptive breaking changes while still giving ourselves some flexibility to flag suspicious code as errors when appropriate. For this reason, we’re continuing with a similar versioning model to that of past releases, so 4.0 is just the natural continuation from TypeScript 3.9,” Daniel Rosenwasser, program manager of TypeScript at Microsoft, wrote in a post

The release candidate for TypeScript 4.0 is expected on August 4, and the final release is scheduled for August 18. 

More information about the new features and breaking changes can be found here