For faster declaration emits, TypeScript now caches whether internal symbols are accessible in different contexts, along with how specific types are to be printed. This improves general performance in code with fairly complex types.
Other performance enhancements in TypeScript 4.4 promise faster path normalisation and path mapping, along with faster incremental builds. Also, an optimisation has been added for source map generation of very large output files.
The TypeScript 4.4 beta can be access through NuGet or via NPM:
npm install typescript@beta
General availability of TypeScript 4.4 is planned for late August, following a release candidate earlier in the month.
Meanwhile for control flow analysis of aliased conditions, when TypeScript sees that a constant value is being tested, it will do extra work to see if it has a type guard. If the type guard operates on a
readonly property, or an unmodified parameter, then TypeScript is able to narrow that value property. Different type guard conditions are preserved, not just
In addition, TypeScript 4.4 is experimenting with editor support for inlay text, which can display information such as parameter names inline in code while index signatures for
symbols and template string patterns now are permitted.
Delving deeper, a new flag,
--useUnknownInCatchVariables, changes the default type of
catch clause variables from
unknown. Another new flag,
--exactOptionalPropertyTypes, specifies that optional property types should be interpreted exactly as written.
TypeScript 4.4 follows the May introduction of the production release of TypeScript 4.3. Among other improvements, the TypeScript 4.3 release allowed developers to specify types for reading and writing to properties.