This document outlines our focused tasks for TypeScript 5.4. It minimally indicates intent to investigate tasks or contribute to an implementation. Nothing is set in stone, but we will strive to complete these tasks in a reasonable timeframe.

gantt
    dateFormat  YYYY-MM-DD
    TypeScript 5.3 Stabilization Period : 2023-11-03, 2023-11-20
    TypeScript 5.4 Beta Development : 2023-11-03, 2024-01-19
    TypeScript 5.4 RC Development : 2024-01-20, 2024-02-16
    TypeScript 5.4 Stabilization Period : 2024-02-16, 2024-03-05
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Compiler and Language

• Type Narrowing for Variables in Closures Occurring After Last Assignments
• The NoInfer Intrinsic
• Isolated Declarations
• Investigate --module preserveand require() in --moduleResolution bundler
• Investigate and Review Regex Syntax Validation
• Checks for Never-Initialized Variables
• Champion throw Expressions
• Investigate Function Implementations Returning Indexed Access and Conditional Types
• Make isTypeAssignableTo public on TypeChecker #56448
• Alleviating Pain-Points around dual-ESM/CJS-published Packages
• Investigate Syntactic Variance Measurement
• Symbol Visibility Walk Optimizations for .d.ts Emit
• Communicate out Plan for 5.0 Deprecations in Anticipation of 5.5

Editor and Language Service

• Define Initial Sketch of LSP Support
• TSServer File-Watching Events
• Organize Imports Respecting type Imports
• Investigate AI-powered Refactorings

Performance

• Investigate Running With V8 Snapshots
• Parallelization Experimentation

Website and Docs

• Author and Iterate on Module Documentation
• Simplify and Refactor Website for Faster Builds

Infrastructure

• Expand Performance Suite
• Move DefinitelyTyped to GitHub Actions
• DefinitelyTyped Monorepo Improvements
• arethetypeswrong validation in DefinitelyTyped