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