What's new in TypeScript

Because this page hit a limit on a GitHub wiki page size, it's now hosted on the website: https://www.typescriptlang.org/docs/handbook/release-notes/overview.html

TypeScript 3.6

See TypeScript 3.6

Stricter Generators

See Stricter Generators

More Accurate Array Spread

See More Accurate Array Spread

Improved UX Around Promises

See Improved UX Around Promises

Better Unicode Support for Identifiers

See Better Unicode Support for Identifiers

import.meta Support in SystemJS

See import.meta Support in SystemJS

get and set Accessors Are Allowed in Ambient Contexts

See get and set Accessors Are Allowed in Ambient Contexts

Ambient Classes and Functions Can Merge

See Ambient Classes and Functions Can Merge

APIs to Support --build and --incremental

See APIs to Support --build and --incremental

Semicolon-Aware Code Edits

See Semicolon-Aware Code Edits

Smarter Auto-Import Syntax

See Smarter Auto-Import Syntax

await Completions on Promises

See await Completions on Promises

New TypeScript Playground

See New TypeScript Playground

TypeScript 3.5

See TypeScript 3.5

Speed improvements

See Speed improvements

Type-checking speed-ups

See Type-checking speed-ups

--incremental improvements

See --incremental improvements

The Omit helper type

See The Omit helper type

Improved excess property checks in union types

See Improved excess property checks in union types

The --allowUmdGlobalAccess flag

See The --allowUmdGlobalAccess flag

Smarter union type checking

See Smarter union type checking

Higher order type inference from generic constructors

See Higher order type inference from generic constructors

TypeScript 3.4

See TypeScript 3.4

Faster subsequent builds with the --incremental flag

See Faster subsequent builds with the --incremental flag

Composite projects

See Composite projects

outFile

See outFile

Higher order type inference from generic functions

See Higher order type inference from generic functions

Improvements for ReadonlyArray and readonly tuples

See Improvements for ReadonlyArray and readonly tuples

A new syntax for ReadonlyArray

See A new syntax for ReadonlyArray

readonly tuples

See readonly tuples

readonly mapped type modifiers and readonly arrays

See readonly mapped type modifiers and readonly arrays

Caveats

See Caveats

const assertions

See const assertions

Caveats

See Caveats

Type-checking for globalThis

See Type-checking for globalThis

TypeScript 3.3

See TypeScript 3.3

Improved behavior for calling union types

See Improved behavior for calling union types

Caveats

See Caveats

Incremental file watching for composite projects in --build --watch

See Incremental file watching for composite projects in --build --watch

TypeScript 3.2

See TypeScript 3.2

strictBindCallApply

See strictBindCallApply

Caveats

See Caveats

Generic spread expressions in object literals

See Generic spread expressions in object literals

Generic object rest variables and parameters

See Generic object rest variables and parameters

BigInt

See BigInt

Caveats

See Caveats

Non-unit types as union discriminants

See Non-unit types as union discriminants

tsconfig.json inheritance via Node.js packages

See tsconfig.json inheritance via Node.js packages

The new --showConfig flag

See The new --showConfig flag

Object.defineProperty declarations in JavaScript

See Object.defineProperty declarations in JavaScript

TypeScript 3.1

See TypeScript 3.1

Mapped types on tuples and arrays

See Mapped types on tuples and arrays

Properties declarations on functions

See Properties declarations on functions

Version selection with typesVersions

See Version selection with typesVersions

Matching behavior

See Matching behavior

Multiple fields

See Multiple fields

TypeScript 3.0

See TypeScript 3.0

Tuples in rest parameters and spread expressions

See Tuples in rest parameters and spread expressions

Rest parameters with tuple types

See Rest parameters with tuple types

Spread expressions with tuple types

See Spread expressions with tuple types

Generic rest parameters

See Generic rest parameters

Example

See Example

Optional elements in tuple types

See Optional elements in tuple types

Example

See Example

Rest elements in tuple types

See Rest elements in tuple types

Example

See Example

New unknown top type

See New unknown top type

Example

See Example

Support for defaultProps in JSX

See Support for defaultProps in JSX

Caveats

See Caveats

Explicit types on defaultProps

See Explicit types on defaultProps

Changes to @types/React

See Changes to @types/React

/// <reference lib="..." /> reference directives

See /// <reference lib="..." /> reference directives

Example

See Example

TypeScript 2.9

See TypeScript 2.9

Support number and symbol named properties with keyof and mapped types

See Support number and symbol named properties with keyof and mapped types

Example

See Example

Example

See Example

Recommendations

See Recommendations

Generic type arguments in JSX elements

See Generic type arguments in JSX elements

Example

See Example

Generic type arguments in generic tagged templates

See Generic type arguments in generic tagged templates

Example

See Example

import types

See import types

Example

See Example

Relaxing declaration emit visiblity rules

See Relaxing declaration emit visiblity rules

Support for import.meta

See Support for import.meta

Example

See Example

New --resolveJsonModule

See New --resolveJsonModule

Example

See Example

--pretty output by default

See --pretty output by default

New --declarationMap

See New --declarationMap

TypeScript 2.8

See TypeScript 2.8

Conditional Types

See Conditional Types

Example

See Example

Distributive conditional types

See Distributive conditional types

Example

See Example

Example

See Example

Example

See Example

Type inference in conditional types

See Type inference in conditional types

Predefined conditional types

See Predefined conditional types

Example

See Example

Improved control over mapped type modifiers

See Improved control over mapped type modifiers

Example

See Example

Example

See Example

Example

See Example

Improved keyof with intersection types

See Improved keyof with intersection types

Example

See Example

Better handling for namespace patterns in .js files

See Better handling for namespace patterns in .js files

IIFEs as namespace declarations

See IIFEs as namespace declarations

Defaulted declarations

See Defaulted declarations

Prototype assignment

See Prototype assignment

Nested and merged declarations

See Nested and merged declarations

Per-file JSX factories

See Per-file JSX factories

Example

See Example

Locally scoped JSX namespaces

See Locally scoped JSX namespaces

New --emitDeclarationsOnly

See New --emitDeclarationsOnly

TypeScript 2.7

See TypeScript 2.7

Constant-named properties

See Constant-named properties

Example

See Example

Example

See Example

unique symbol

See unique symbol

Example

See Example

Example

See Example

Strict Class Initialization

See Strict Class Initialization

Definite Assignment Assertions

See Definite Assignment Assertions

Fixed Length Tuples

See Fixed Length Tuples

Improved type inference for object literals

See Improved type inference for object literals

Example

See Example

Improved handling of structurally identical classes and instanceof expressions

See Improved handling of structurally identical classes and instanceof expressions

Example:

See Example:

Type guards inferred from in operator

See Type guards inferred from in operator

Example

See Example

Support for import d from "cjs" form CommonJS modules with --esModuleInterop

See Support for import d from "cjs" form CommonJS modules with --esModuleInterop

Example

See Example

Numeric separators

See Numeric separators

Example

See Example

Cleaner output in --watch mode

See Cleaner output in --watch mode

Prettier --pretty output

See Prettier --pretty output

TypeScript 2.6

See TypeScript 2.6

Strict function types

See Strict function types

Example

See Example

Note:

See Note:

Support for JSX Fragment Syntax

See Support for JSX Fragment Syntax

Cache tagged template objects in modules

See Cache tagged template objects in modules

Example

See Example

Localized diagnostics on the command line

See Localized diagnostics on the command line

Example

See Example

Suppress errors in .ts files using '// @ts-ignore' comments

See Suppress errors in .ts files using '// @ts-ignore' comments

Example

See Example

Faster tsc --watch

See Faster tsc --watch

Write-only references now flagged as unused

See Write-only references now flagged as unused

Example

See Example

Example

See Example

TypeScript 2.5

See TypeScript 2.5

Optional catch clause variables

See Optional catch clause variables

Type assertion/cast syntax in checkJs/@ts-check mode

See Type assertion/cast syntax in checkJs/@ts-check mode

Deduplicated and redirected packages

See Deduplicated and redirected packages

The --preserveSymlinks compiler flag

See The --preserveSymlinks compiler flag

TypeScript 2.4

See TypeScript 2.4

Dynamic Import Expressions

See Dynamic Import Expressions

String Enums

See String Enums

Improved inference for generics

See Improved inference for generics

Return types as inference targets

See Return types as inference targets

Type parameter inference from contextual types

See Type parameter inference from contextual types

Stricter checking for generic functions

See Stricter checking for generic functions

Strict contravariance for callback parameters

See Strict contravariance for callback parameters

Weak Type Detection

See Weak Type Detection

TypeScript 2.3

See TypeScript 2.3

Generators and Iteration for ES5/ES3

See Generators and Iteration for ES5/ES3

Iterators

See Iterators

Generators

See Generators

New --downlevelIteration

See New --downlevelIteration

Async Iteration

See Async Iteration

Async iterators

See Async iterators

Async Generators

See Async Generators

The for-await-of Statement

See The for-await-of Statement

Caveats

See Caveats

Generic parameter defaults

See Generic parameter defaults

Example

See Example

New --strict master option

See New --strict master option

Enhanced --init output

See Enhanced --init output

Errors in .js files with --checkJs

See Errors in .js files with --checkJs

TypeScript 2.2

See TypeScript 2.2

Support for Mix-in classes

See Support for Mix-in classes

First some terminology:

See First some terminology:

Putting all of the above rules together in an example:

See Putting all of the above rules together in an example:

object type

See object type

Support for new.target

See Support for new.target

Example

See Example

Better checking for null/undefined in operands of expressions

See Better checking for null/undefined in operands of expressions

Dotted property for types with string index signatures

See Dotted property for types with string index signatures

Support for spread operator on JSX element children

See Support for spread operator on JSX element children

Example

See Example

New jsx: react-native

See New jsx: react-native

TypeScript 2.1

See TypeScript 2.1

keyof and Lookup Types

See keyof and Lookup Types

Example

See Example

Example

See Example

Mapped Types

See Mapped Types

Partial, Readonly, Record, and Pick

See Partial, Readonly, Record, and Pick

Object Spread and Rest

See Object Spread and Rest

Downlevel Async Functions

See Downlevel Async Functions

Example

See Example

tsconfig.json

See tsconfig.json

dramaticWelcome.ts

See dramaticWelcome.ts

Support for external helpers library (tslib)

See Support for external helpers library (tslib)

Untyped imports

See Untyped imports

Example

See Example

Support for --target ES2016, --target ES2017 and --target ESNext

See Support for --target ES2016, --target ES2017 and --target ESNext

Improved any Inference

See Improved any Inference

Example

See Example

Implicit any errors

See Implicit any errors

Example

See Example

Better inference for literal types

See Better inference for literal types

Example

See Example

Example

See Example

Use returned values from super calls as 'this'

See Use returned values from super calls as 'this'

Example

See Example

Configuration inheritance

See Configuration inheritance

Example

See Example

New --alwaysStrict

See New --alwaysStrict

TypeScript 2.0

See TypeScript 2.0

Null- and undefined-aware types

See Null- and undefined-aware types

--strictNullChecks

See --strictNullChecks

Example

See Example

Assigned-before-use checking

See Assigned-before-use checking

Example

See Example

Optional parameters and properties

See Optional parameters and properties

Non-null and non-undefined type guards

See Non-null and non-undefined type guards

Example

See Example

Dotted names in type guards

See Dotted names in type guards

Example

See Example

Expression operators

See Expression operators

Type widening

See Type widening

Non-null assertion operator

See Non-null assertion operator

Compatibility

See Compatibility

Control flow based type analysis

See Control flow based type analysis

Example

See Example

Tagged union types

See Tagged union types

Example

See Example

The never type

See The never type

Read-only properties and index signatures

See Read-only properties and index signatures

Example

See Example

Specifying the type of this for functions

See Specifying the type of this for functions

this parameters in callbacks

See this parameters in callbacks

Example

See Example

--noImplicitThis

See --noImplicitThis

Glob support in tsconfig.json

See Glob support in tsconfig.json

Example

See Example

Module resolution enhancements: BaseUrl, Path mapping, rootDirs and tracing

See Module resolution enhancements: BaseUrl, Path mapping, rootDirs and tracing

Base URL

See Base URL

Example

See Example

Path mapping

See Path mapping

Example

See Example

Virtual Directories with rootDirs

See Virtual Directories with rootDirs

Example

See Example

Tracing module resolution

See Tracing module resolution

Shorthand ambient module declarations

See Shorthand ambient module declarations

declarations.d.ts

See declarations.d.ts

Wildcard character in module names

See Wildcard character in module names

Example

See Example

Example

See Example

Support for UMD module definitions

See Support for UMD module definitions

math-lib.d.ts

See math-lib.d.ts

Optional class properties

See Optional class properties

Example

See Example

Private and Protected Constructors

See Private and Protected Constructors

Example

See Example

Abstract properties and accessors

See Abstract properties and accessors

Example

See Example

Implicit index signatures

See Implicit index signatures

Including built-in type declarations with --lib

See Including built-in type declarations with --lib

Example

See Example

Flag unused declarations with --noUnusedParameters and --noUnusedLocals

See Flag unused declarations with --noUnusedParameters and --noUnusedLocals

Example

See Example

Module identifiers allow for .js extension

See Module identifiers allow for .js extension

Support 'target : es5' with 'module: es6'

See Support 'target : es5' with 'module: es6'

Trailing commas in function parameter and argument lists

See Trailing commas in function parameter and argument lists

Example

See Example

New --skipLibCheck

See New --skipLibCheck

Allow duplicate identifiers across declarations

See Allow duplicate identifiers across declarations

Example

See Example

New --declarationDir

See New --declarationDir

TypeScript 1.8

See TypeScript 1.8

Type parameters as constraints

See Type parameters as constraints

Example

See Example

Control flow analysis errors

See Control flow analysis errors

Unreachable code

See Unreachable code

Example

See Example

Unused labels

See Unused labels

Example

See Example

Implicit returns

See Implicit returns

Example

See Example

Case clause fall-throughs

See Case clause fall-throughs

Example

See Example

Stateless Function Components in React

See Stateless Function Components in React

Simplified props type management in React

See Simplified props type management in React

Augmenting global/module scope from modules

See Augmenting global/module scope from modules

Example

See Example

Example

See Example

String literal types

See String literal types

Improved union/intersection type inference

See Improved union/intersection type inference

Example

See Example

Concatenate AMD and System modules with --outFile

See Concatenate AMD and System modules with --outFile

Example

See Example

Support for default import interop with SystemJS

See Support for default import interop with SystemJS

Allow captured let/const in loops

See Allow captured let/const in loops

Example

See Example

Improved checking for for..in statements

See Improved checking for for..in statements

Example

See Example

Modules are now emitted with a "use strict"; prologue

See Modules are now emitted with a "use strict"; prologue

Including .js files with --allowJs

See Including .js files with --allowJs

Custom JSX factories using --reactNamespace

See Custom JSX factories using --reactNamespace

Example

See Example

this-based type guards

See this-based type guards

Example

See Example

Official TypeScript NuGet package

See Official TypeScript NuGet package

Prettier error messages from tsc

See Prettier error messages from tsc

Colorization of JSX code in VS 2015

See Colorization of JSX code in VS 2015

The --project (-p) flag can now take any file path

See The --project (-p) flag can now take any file path

Allow comments in tsconfig.json

See Allow comments in tsconfig.json

Support output to IPC-driven files

See Support output to IPC-driven files

Improved support for tsconfig.json in Visual Studio 2015

See Improved support for tsconfig.json in Visual Studio 2015

A couple of limitations:

See A couple of limitations:

TypeScript 1.7

See TypeScript 1.7

async/await support in ES6 targets (Node v4+)

See async/await support in ES6 targets (Node v4+)

Example

See Example

Support for --target ES6 with --module

See Support for --target ES6 with --module

Example

See Example

this-typing

See this-typing

ES7 exponentiation operator

See ES7 exponentiation operator

Example

See Example

Improved checking for destructuring object literal

See Improved checking for destructuring object literal

Example

See Example

Support for decorators when targeting ES3

See Support for decorators when targeting ES3

TypeScript 1.6

See TypeScript 1.6

JSX support

See JSX support

New .tsx file extension and as operator

See New .tsx file extension and as operator

Using React

See Using React

Using other JSX frameworks

See Using other JSX frameworks

Output generation

See Output generation

Intersection types

See Intersection types

Example

See Example

Local type declarations

See Local type declarations

Class expressions

See Class expressions

Extending expressions

See Extending expressions

abstract classes and methods

See abstract classes and methods

Examples

See Examples

Generic type aliases

See Generic type aliases

Stricter object literal assignment checks

See Stricter object literal assignment checks

Examples

See Examples

ES6 generators

See ES6 generators

Experimental support for async functions

See Experimental support for async functions

Example

See Example

Nightly builds

See Nightly builds

Adjustments in module resolution logic

See Adjustments in module resolution logic

Merging ambient class and interface declaration

See Merging ambient class and interface declaration

User-defined type guard functions

See User-defined type guard functions

Examples

See Examples

exclude property support in tsconfig.json

See exclude property support in tsconfig.json

--init command line option

See --init command line option

TypeScript 1.5

See TypeScript 1.5

ES6 Modules

See ES6 Modules ##

Export Declarations

See Export Declarations

Re-exporting

See Re-exporting

Default Export

See Default Export

Bare Import

See Bare Import

Destructuring in declarations and assignments

See Destructuring in declarations and assignments

Declarations

See Declarations

Assignments

See Assignments

namespace keyword

See namespace keyword

let and const support

See let and const support

Const

See Const

Block scoped

See Block scoped

for..of support

See for..of support

Example

See Example

Decorators

See Decorators

Example

See Example

Computed properties

See Computed properties

Support for UMD and System module output

See Support for UMD and System module output

Unicode codepoint escapes in strings

See Unicode codepoint escapes in strings

Tagged template strings in ES3/ES5

See Tagged template strings in ES3/ES5

AMD-dependency optional names

See AMD-dependency optional names

Project support through tsconfig.json

See Project support through tsconfig.json

Example

See Example

--rootDir command line option

See --rootDir command line option

--noEmitHelpers command line option

See --noEmitHelpers command line option

--newLine command line option

See --newLine command line option

--inlineSourceMap and inlineSources command line options

See --inlineSourceMap and inlineSources command line options

TypeScript 1.4

See TypeScript 1.4

Union types

See Union types

Overview

See Overview

Stricter Generics

See Stricter Generics

Better Type Inference

See Better Type Inference

let declarations

See let declarations

const declarations

See const declarations

Template strings

See Template strings

Type Guards

See Type Guards

Type Aliases

See Type Aliases

const enum (completely inlined enums)

See const enum (completely inlined enums)

-noEmitOnError commandline option

See -noEmitOnError commandline option

AMD Module names

See AMD Module names

TypeScript 1.3

See TypeScript 1.3

Protected

See Protected

Tuple types

See Tuple types

TypeScript 1.1

See TypeScript 1.1

Performance Improvements

See Performance Improvements

Better Module Visibility Rules

See Better Module Visibility Rules