• TypeScript 4.9
• Better Types for Promise.resolve
• JavaScript Emit No Longer Elides Imports
• exports is Prioritized Over typesVersions
• TypeScript 4.8
• Unconstrained Type Parameters No Longer Assignable to {} in strictNullChecks
• TypeScript 4.7
• Stricter Spread Checks in JSX
• Stricter Checks with Template String Expressions
• readFile Method is No Longer Optional on LanguageServiceHost
• readonly Tuples Have a readonlylength Property
• TypeScript 4.6
• Object Rests Drop Unspreadable Members from Generic Objects
• JavaScript Files Always Receive Grammar and Binding Errors
• TypeScript 4.5
• lib.d.ts Changes for TypeScript 4.5
• Inference Changes from Awaited
• Template Strings Use .concat()
• Compiler Options Checking at the Root of tsconfig.json
• Restrictions on Assignability to Conditional Types
• TypeScript 4.4
• lib.d.ts Changes for TypeScript 4.4
• More-Compliant Indirect Calls for Imported Functions
• Using unknown in Catch Variables
• Broader Always-Truthy Promise Checks
• Abstract Properties Do Not Allow Initializers
• TypeScript 4.3
• Union Enums Cannot Be Compared to Arbitrary Numbers
• TypeScript 4.2
• noImplicitAny Errors Apply to Loose yield Expressions
• Type Arguments in JavaScript Are Not Parsed as Type Arguments
• The in Operator No Longer Allows Primitive Types on the Right Side
• TypeScript 4.1
• abstract Members Can't Be Marked async
• resolve's Parameters Are No Longer Optional in Promises
• any and unknown are considered possibly falsy in && expressions
• Conditional Spreads Create Optional Properties
• Unmatched parameters are no longer related
• TypeScript 4.0
• Properties Overridding Accessors (and vice versa) is an Error
• Operands for delete must be optional.
• TypeScript 3.9
• Parsing Differences in Optional Chaining and Non-Null Assertions
• } and > are Now Invalid JSX Text Characters
• Stricter Checks on Intersections and Optional Properties
• Intersections Reduced By Discriminant Properties
• Getters/Setters are No Longer Enumerable
• Type Parameters That Extend any No Longer Act as any
• export * is Always Retained
• Exports Now Use Getters for Live Bindings
• Exports are Hoisted and Initially Assigned
• TypeScript 3.8
• Stricter Assignability Checks to Unions with Index Signatures
• Optional Arguments with no Inferences are Correctly Marked as Implicitly any
• object in JSDoc is No Longer any Under noImplicitAny
• TypeScript 3.6
• Class Members Named "constructor" Are Now Constructors
• DOM Updates
• JSDoc Comments No Longer Merge
• Keywords Cannot Contain Escape Sequences
• TypeScript 3.5
• Generic type parameters are implicitly constrained to unknown
• { [k: string]: unknown } is no longer a wildcard assignment target
• Improved excess property checks in union types
• Background
• Rationale and Change
• Workarounds
• Fixes to Unsound Writes to Indexed Access Types
• Background
• Change and Rationale
• Workarounds
• lib.d.ts includes the Omit helper type
• Object.keys rejects primitives in ES5
• Background
• Rationale and Change
• Workarounds
• TypeScript 3.4
• Top-level this is now typed
• Propagated generic type arguments
• Contextual return types flow in as contextual argument types
• Consistent inference priorities outside of strictFunctionTypes
• TypeScript 3.2
• lib.d.ts updates
• wheelDelta and friends have been removed.
• More specific types
• TypeScript 3.1
• Some vendor-specific types are removed from lib.d.ts
• Recommendations:
• Narrowing functions now intersects {}, Object, and unconstrained generic type parameters.
• TypeScript 3.0
• The unknown keyword is reserved
• Intersecting with null/undefined reduces to null/undefined outside of strictNullChecks
• Recommendation
• TypeScript 2.9
• keyof now includes string, number and symbol keys
• Recommendations:
• Trailing commas not allowed on rest parameters
• In strictNullChecks, an unconstrained type parameter is no longer assignable to object
• TypeScript 2.8
• Unused type parameters are checked under --noUnusedParameters
• Some MS-specific types are removed from lib.d.ts
• HTMLObjectElement no longer has an alt attribute
• TypeScript 2.7
• Tuples now have a fixed length property
• Under allowSyntheticDefaultImports, types for default imports are synthesized less often for TS and JS files
• Stricter checking for indexed access generic type constraints
• in expressions are treated as type guards
• Structurally-equivalent classes are not reduced in conditional operator
• CustomEvent is now a generic type
• TypeScript 2.6
• Write-only references are unused
• Arbitrary expressions are forbidden in export assignments in ambient contexts
• TypeScript 2.4
• Weak Type Detection
• Return types as inference targets
• Stricter variance in callback parameters
• Promises
• (Nested) Callbacks
• Stricter checking for generic functions
• Type parameter inference from contextual types
• TypeScript 2.3
• Empty generic parameter lists are flagged as error
• TypeScript 2.2
• Changes to DOM API's in the standard library
• TypeScript 2.1
• Generated constructor code substitutes the return value of super(...) calls as this
• Extending built-ins like Error, Array, and Map may no longer work
• Literal types are inferred by default for const variables and readonly properties
• No type narrowing for captured variables in functions and class expressions
• Implicit-any error raised for un-annotated callback arguments with no matching overload arguments
• Comma operators on side-effect-free expressions is now flagged as an error
• Changes to DOM API's in the standard library
• TypeScript 2.0
• No type narrowing for captured variables in functions and class expressions
• Generic type parameters are now narrowed
• Getters with no setters are automatically inferred to be readonly properties
• Function declarations not allowed in blocks in strict mode
• TemplateStringsArray is now immutable
• TypeScript 1.8
• Modules are now emitted with a "use strict"; prologue
• Exporting non-local names from a module
• Reachability checks are enabled by default
• --module is not allowed alongside --outFile unless --module is specified as one of amd or system.
• Changes to DOM API's in the standard library
• Disallow this accessing before super-call
• TypeScript 1.7
• Changes in inferring the type from this
• Automatic semicolon insertion after class member modifiers
• TypeScript 1.6
• Strict object literal assignment checking
• CommonJS module resolution no longer assumes paths are relative
• Function and class default export declarations can no longer merge with entities intersecting in their meaning
• Module bodies are parsed in strict mode
• Changes to DOM API's in the standard library
• System module output uses bulk exports
• .js content of npm package is moved from 'bin' to 'lib' folder
• TypeScript npm package does not install globally by default
• Decorators are checked as call expressions
• TypeScript 1.5
• Referencing arguments in arrow functions is not allowed
• Enum reference in-lining changes
• Contextual type flows through super and parenthesized expressions
• DOM interface changes
• Class bodies are parsed in strict mode
• TypeScript 1.4
• Multiple Best Common Type Candidates
• Generic Type Inference
• Generic Rest Parameters
• Overload Resolution with Type Argument Inference
• Strict Mode Parsing for Class Declarations and Class Expressions
• TypeScript 1.1
• Working with null and undefined in ways that are observably incorrect is now an error