TypeScript 3.6
Stricter Generators
More Accurate Array Spread
Improved UX Around Promises
Better Unicode Support for Identifiers
import.meta Support in SystemJS
get and set Accessors Are Allowed in Ambient Contexts
Ambient Classes and Functions Can Merge
APIs to Support --build and --incremental
Semicolon-Aware Code Edits
Smarter Auto-Import Syntax
await Completions on Promises
New TypeScript Playground
TypeScript 3.5
Speed improvements
Type-checking speed-ups
--incremental improvements
The Omit helper type
Improved excess property checks in union types
The --allowUmdGlobalAccess flag
Smarter union type checking
Higher order type inference from generic constructors
TypeScript 3.4
Faster subsequent builds with the --incremental flag
Composite projects
outFile
Higher order type inference from generic functions
Improvements for ReadonlyArray and readonly tuples
A new syntax for ReadonlyArray
readonly tuples
readonly mapped type modifiers and readonly arrays
Caveats
const assertions
Caveats
Type-checking for globalThis
TypeScript 3.3
Improved behavior for calling union types
Caveats
Incremental file watching for composite projects in --build --watch
TypeScript 3.2
strictBindCallApply
Caveats
Generic spread expressions in object literals
Generic object rest variables and parameters
BigInt
Caveats
Non-unit types as union discriminants
tsconfig.json inheritance via Node.js packages
The new --showConfig flag
Object.defineProperty declarations in JavaScript
TypeScript 3.1
Mapped types on tuples and arrays
Properties declarations on functions
Version selection with typesVersions
Matching behavior
Multiple fields
TypeScript 3.0
Tuples in rest parameters and spread expressions
Rest parameters with tuple types
Spread expressions with tuple types
Generic rest parameters
Example
Optional elements in tuple types
Example
Rest elements in tuple types
Example
New unknown top type
Example
Support for defaultProps in JSX
Caveats
Explicit types on defaultProps
Changes to @types/React
/// <reference lib="..." /> reference directives
Example
TypeScript 2.9
Support number and symbol named properties with keyof and mapped types
Example
Example
Recommendations
Generic type arguments in JSX elements
Example
Generic type arguments in generic tagged templates
Example
import types
Example
Relaxing declaration emit visiblity rules
Support for import.meta
Example
New --resolveJsonModule
Example
--pretty output by default
New --declarationMap
TypeScript 2.8
Conditional Types
Example
Distributive conditional types
Example
Example
Example
Type inference in conditional types
Predefined conditional types
Example
Improved control over mapped type modifiers
Example
Example
Example
Improved keyof with intersection types
Example
Better handling for namespace patterns in .js files
IIFEs as namespace declarations
Defaulted declarations
Prototype assignment
Nested and merged declarations
Per-file JSX factories
Example
Locally scoped JSX namespaces
New --emitDeclarationsOnly
TypeScript 2.7
Constant-named properties
Example
Example
unique symbol
Example
Example
Strict Class Initialization
Definite Assignment Assertions
Fixed Length Tuples
Improved type inference for object literals
Example
Improved handling of structurally identical classes and instanceof expressions
Example:
Type guards inferred from in operator
Example
Support for import d from "cjs" form CommonJS modules with --esModuleInterop
Example
Numeric separators
Example
Cleaner output in --watch mode
Prettier --pretty output
TypeScript 2.6
Strict function types
Example
Note:
Support for JSX Fragment Syntax
Cache tagged template objects in modules
Example
Localized diagnostics on the command line
Example
Suppress errors in .ts files using '// @ts-ignore' comments
Example
Faster tsc --watch
Write-only references now flagged as unused
Example
Example
TypeScript 2.5
Optional catch clause variables
Type assertion/cast syntax in checkJs/@ts-check mode
Deduplicated and redirected packages
The --preserveSymlinks compiler flag
TypeScript 2.4
Dynamic Import Expressions
String Enums
Improved inference for generics
Return types as inference targets
Type parameter inference from contextual types
Stricter checking for generic functions
Strict contravariance for callback parameters
Weak Type Detection
TypeScript 2.3
Generators and Iteration for ES5/ES3
Iterators
Generators
New --downlevelIteration
Async Iteration
Async iterators
Async Generators
The for-await-of Statement
Caveats
Generic parameter defaults
Example
New --strict master option
Enhanced --init output
Errors in .js files with --checkJs
TypeScript 2.2
Support for Mix-in classes
First some terminology:
Putting all of the above rules together in an example:
object type
Support for new.target
Example
Better checking for null/undefined in operands of expressions
Dotted property for types with string index signatures
Support for spread operator on JSX element children
Example
New jsx: react-native
TypeScript 2.1
keyof and Lookup Types
Example
Example
Mapped Types
Partial, Readonly, Record, and Pick
Object Spread and Rest
Downlevel Async Functions
Example
tsconfig.json
dramaticWelcome.ts
Support for external helpers library (tslib)
Untyped imports
Example
Support for --target ES2016, --target ES2017 and --target ESNext
Improved any Inference
Example
Implicit any errors
Example
Better inference for literal types
Example
Example
Use returned values from super calls as 'this'
Example
Configuration inheritance
Example
New --alwaysStrict
TypeScript 2.0
Null- and undefined-aware types
--strictNullChecks
Example
Assigned-before-use checking
Example
Optional parameters and properties
Non-null and non-undefined type guards
Example
Dotted names in type guards
Example
Expression operators
Type widening
Non-null assertion operator
Compatibility
Control flow based type analysis
Example
Tagged union types
Example
The never type
Read-only properties and index signatures
Example
Specifying the type of this for functions
this parameters in callbacks
Example
--noImplicitThis
Glob support in tsconfig.json
Example
Module resolution enhancements: BaseUrl, Path mapping, rootDirs and tracing
Base URL
Example
Path mapping
Example
Virtual Directories with rootDirs
Example
Tracing module resolution
Shorthand ambient module declarations
declarations.d.ts
Wildcard character in module names
Example
Example
Support for UMD module definitions
math-lib.d.ts
Optional class properties
Example
Private and Protected Constructors
Example
Abstract properties and accessors
Example
Implicit index signatures
Including built-in type declarations with --lib
Example
Flag unused declarations with --noUnusedParameters and --noUnusedLocals
Example
Module identifiers allow for .js extension
Support 'target : es5' with 'module: es6'
Trailing commas in function parameter and argument lists
Example
New --skipLibCheck
Allow duplicate identifiers across declarations
Example
New --declarationDir
TypeScript 1.8
Type parameters as constraints
Example
Control flow analysis errors
Unreachable code
Example
Unused labels
Example
Implicit returns
Example
Case clause fall-throughs
Example
Stateless Function Components in React
Simplified props type management in React
Augmenting global/module scope from modules
Example
Example
String literal types
Improved union/intersection type inference
Example
Concatenate AMD and System modules with --outFile
Example
Support for default import interop with SystemJS
Allow captured let/const in loops
Example
Improved checking for for..in statements
Example
Modules are now emitted with a "use strict"; prologue
Including .js files with --allowJs
Custom JSX factories using --reactNamespace
Example
this-based type guards
Example
Official TypeScript NuGet package
Prettier error messages from tsc
Colorization of JSX code in VS 2015
The --project (-p) flag can now take any file path
Allow comments in tsconfig.json
Support output to IPC-driven files
Improved support for tsconfig.json in Visual Studio 2015
A couple of limitations:
TypeScript 1.7
async/await support in ES6 targets (Node v4+)
Example
Support for --target ES6 with --module
Example
this-typing
ES7 exponentiation operator
Example
Improved checking for destructuring object literal
Example
Support for decorators when targeting ES3
TypeScript 1.6
JSX support
New .tsx file extension and as operator
Using React
Using other JSX frameworks
Output generation
Intersection types
Example
Local type declarations
Class expressions
Extending expressions
abstract classes and methods
Examples
Generic type aliases
Stricter object literal assignment checks
Examples
ES6 generators
Experimental support for async functions
Example
Nightly builds
Adjustments in module resolution logic
Merging ambient class and interface declaration
User-defined type guard functions
Examples
exclude property support in tsconfig.json
--init command line option
TypeScript 1.5
ES6 Modules
Export Declarations
Re-exporting
Default Export
Bare Import
Destructuring in declarations and assignments
Declarations
Assignments
namespace keyword
let and const support
Const
Block scoped
for..of support
Example
Decorators
Example
Computed properties
Support for UMD and System module output
Unicode codepoint escapes in strings
Tagged template strings in ES3/ES5
AMD-dependency optional names
Project support through tsconfig.json
Example
--rootDir command line option
--noEmitHelpers command line option
--newLine command line option
--inlineSourceMap and inlineSources command line options
TypeScript 1.4
Union types
Overview
Stricter Generics
Better Type Inference
let declarations
const declarations
Template strings
Type Guards
Type Aliases
const enum (completely inlined enums)
-noEmitOnError commandline option
AMD Module names
TypeScript 1.3
Protected
Tuple types
TypeScript 1.1
Performance Improvements
Better Module Visibility Rules