●Change8

v5.8-rc

Breaking Changes
📦 typescriptView on GitHub →
⚠ 2 breaking✨ 5 features🐛 1 fixes⚡ 1 deprecations🔧 6 symbols

Summary

TypeScript 5.8 introduces the --erasableSyntaxOnly flag, improves type checking for conditional return expressions, and updates import attribute requirements to align with modern Node.js standards.

⚠️ Breaking Changes

  • Restrictions on Import Assertions: The legacy 'assert' syntax for import attributes now triggers an error when used with 'type: module' in Node.js. Use the 'with' keyword instead.
  • Stricter checks for 'use strict' in modules: TypeScript now correctly identifies that modules are always in strict mode, which may surface new errors in code that previously relied on non-strict behavior.

Migration Steps

  1. Update import attribute syntax from 'assert { type: "json" }' to 'with { type: "json" }'.
  2. If using --erasableSyntaxOnly, refactor code to remove enums, namespaces, and constructor parameter properties.
  3. Review return statements where conditional logic was previously inferred as a union of types.

✨ New Features

  • Granular Evaluation of Branching in Return Expressions: Improved type inference for conditional (ternary) operators and logical expressions in return statements.
  • Support for --module node18: A new module target to specifically match Node.js 18 behavior.
  • The --erasableSyntaxOnly flag: Ensures TypeScript files only use syntax that can be easily stripped (no enums, namespaces, or parameter properties) for faster builds.
  • Improved Support for require() of ECMAScript Modules in Node.js: Better interoperability when loading ESM from CJS under specific Node.js flags.
  • Preserved Computed Property Names: TypeScript now preserves the literal types of computed property names in classes and object literals more accurately.

🐛 Bug Fixes

  • Fixed various issues related to milestone 5.8.0 (Beta) and 5.8.1 (RC) as tracked in the GitHub issue tracker.

🔧 Affected Symbols

--module--erasableSyntaxOnlyimportrequireassertwith

⚡ Deprecations

  • The 'assert' keyword in import attributes is deprecated in favor of 'with'.