microsoft/TypeScript typescript

Version: 6.0.0-beta (4 months ago) Tags: dev: 3.9.4 (5 years ago), tag-for-publishing-older-releases: 4.1.6 (4 years ago), insiders: 4.6.2-insiders.20220225 (3 years ago), rc: 5.9.1-rc (6 months ago), latest: 5.9.3 (4 months ago), beta: 6.0.0-beta (2 days ago), next: 6.0.0-dev.20260213 (today)

References: package.json — exports, entry points • README — setup, basic usage • GitHub Issues — bugs, workarounds, edge cases • Releases — changelog, breaking changes, new APIs

Search

Use npx -y skilld search instead of grepping .skilld/ directories — hybrid semantic + keyword search across all indexed docs, issues, and releases.

npx -y skilld search "query" -p typescript
npx -y skilld search "issues:error handling" -p typescript
npx -y skilld search "releases:deprecated" -p typescript

Filters: docs:, issues:, releases: prefix narrows by source type.

API Changes

⚠️ erasableSyntaxOnly — new in v6.0, when enabled disallows runtime-emitted TS syntax (enums, namespaces, parameter properties, non-declare class fields with useDefineForClassFields: false); required for --noEmit + Node.js --experimental-strip-types workflows source

⚠️ ModuleKind.None / AMD / UMD / System — deprecated in v6.0, use ES2015+ / Node16+ / NodeNext / Preserve instead source

✨ ModuleKind.Node18 / Node20 — new in v6.0, target specific Node.js version module semantics (alongside existing Node16 and NodeNext) source

✨ noCheck — new compiler option (v5.6+), skips type checking entirely while still emitting declarations/JS; replaces skipLibCheck for full-skip use cases source

✨ isolatedDeclarations — new in v5.5, requires annotations on exported declarations so .d.ts can be generated without type checking (enables parallel declaration emit) source

⚠️ ImportClause API changed — createImportClause(isTypeOnly, name, namedBindings) deprecated, use createImportClause(phaseModifier, name, namedBindings) where phaseModifier is SyntaxKind.TypeKeyword | SyntaxKind.DeferKeyword | undefined; DeferKeyword supports deferred import evaluation proposal source

⚠️ AssertClause/AssertEntry — deprecated, renamed to ImportAttributes/ImportAttribute; assert keyword replaced by with keyword (import x from 'y' with { type: 'json' }) source

✨ rewriteRelativeImportExtensions — new in v5.7, rewrites .ts/.tsx/.mts/.cts extensions in relative imports to .js/.jsx/.mjs/.cjs in output; enables writing .ts extensions in source source

✨ noUncheckedSideEffectImports — new in v5.6, reports errors on bare import 'module' statements when the module can't be resolved source

✨ NoInfer<T> — new intrinsic utility type (v5.4+), prevents inference from a type parameter position; use to force explicit type arguments instead of accidental widening source

⚠️ ScriptTarget.ES3 / ES5 — deprecated, minimum recommended target is ES2015+ source

✨ Promise.try() — new in lib.es2025.promise, wraps sync/async callbacks into a Promise: Promise.try(() => mayThrow()) source

✨ RegExp.escape() — new in lib.es2025.regexp, escapes regex metacharacters: new RegExp(RegExp.escape(userInput)) source

✨ Iterator.from() / IteratorObject helpers — new in lib.es2025.iterator, built-in .map(), .filter(), .take(), .drop(), .flatMap(), .reduce(), .toArray(), .forEach() on iterators source

⚠️ verbatimModuleSyntax — v5.5+ replaces both importsNotUsedAsValues (deprecated) and preserveValueImports (deprecated); use import type explicitly or enable this flag source

Best Practices

✅ Set erasableSyntaxOnly: true for Node.js --experimental-strip-types compatibility — ensures no TypeScript syntax that requires runtime emit (enums, namespaces, parameter properties) source

✅ Use noCheck: true to skip type-checking while still emitting .d.ts and .js — useful for fast builds when editor already reports errors source

✅ Use verbatimModuleSyntax: true instead of deprecated importsNotUsedAsValues and preserveValueImports — enforces explicit import type for type-only imports source

✅ Target "ES2025" to get Set methods, Promise.try, Iterator helpers, RegExp.escape, Map.getOrInsert, and Float16Array without polyfills source

{ "compilerOptions": { "target": "ES2025", "lib": ["ES2025"] } }

✅ Use Map.getOrInsert/getOrInsertComputed instead of has()-then-set() pattern — atomic get-or-create avoids race conditions and redundant lookups (lib "ESNext") source

const cache = new Map<string, Item[]>()
cache.getOrInsertComputed(key, () => []).push(item)

✅ Use using/await using with DisposableStack for deterministic cleanup — replaces try/finally for file handles, connections, event listeners (lib "ESNext.Disposable") source

using stack = new DisposableStack()
const conn = stack.use(getConnection())
const sub = stack.adopt(emitter, e => e.removeAllListeners())
stack.defer(() => cleanup())

✅ Prefer Promise.try() over new Promise(resolve => resolve(fn())) — wraps sync-or-async callbacks into promises without boilerplate (lib "ES2025.Promise") source

✅ Use Uint8Array.fromBase64()/.toBase64() instead of btoa/atob — handles binary data directly without string encoding issues, supports base64url alphabet (lib "ESNext.TypedArrays") source

✅ Use customConditions to resolve package.json exports with custom conditions — enables framework-specific entry points (e.g., "react-server") without bundler hacks source