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TypeScript 7 — Types, Compiler & Migration

The type system and the native TypeScript 7 compiler, with a practical path from modelling values to faster builds.

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31
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6

Compiler

What TypeScript 7 is

Move to the native compiler while keeping the familiar tsc workflow and type-checking model.

  • The native compiler changes implementation rather than JavaScript runtime behavior.
  • Validate diagnostics and emitted output against the previous toolchain.
  • Check build and editor integration support before migration.

tsc and project references

Split large repositories into buildable projects and let the compiler reuse work safely.

  • Declare project references to express build dependencies.
  • Use build mode to check referenced projects in dependency order.
  • Keep generated outputs and source boundaries explicit.

Compiler API compatibility

Identify tools that still need the TypeScript 6 API while the TypeScript 7 compiler matures.

  • A native compiler is not a drop-in JavaScript Compiler API object.
  • Inventory tools that import the typescript package at runtime.
  • Keep a compatible toolchain for integrations awaiting native support.

Parallel builds

Tune TypeScript 7's native parallelism for faster checks in large repositories.

  • Benchmark native compiler performance on representative repositories.
  • Track memory and wall time under the available CPU budget.
  • Check reproducibility before tuning parallel execution settings.

Build mode and incremental checks

Use project build mode and incremental state to shorten repeated checks in monorepos.

  • Build mode coordinates referenced project outputs.
  • Incremental metadata lets compatible builds reuse previous work.
  • Invalidate or rebuild when configuration and dependencies change.

TypeScript language service

Understand editor diagnostics, navigation and tooling versions when adopting the native compiler.

  • Align the editor's TypeScript tooling with the project version.
  • Verify completion, navigation and refactoring during compiler upgrades.
  • Keep editor integration compatibility separate from command-line success.

Type system

Unions and narrowing

Represent alternatives and let control flow refine a value to the safe branch.

  • Use a union to represent several possible value shapes.
  • Narrow with discriminants, typeof or runtime checks.
  • Handle every branch before accessing variant-specific fields.

Generics

Preserve relationships between inputs and outputs instead of falling back to any.

  • Introduce type parameters where inputs and outputs are related.
  • Add constraints only for capabilities the implementation needs.
  • Prefer inference over unnecessary explicit type arguments.

Intersection types

Compose capabilities from several object types while understanding conflicting properties.

  • An intersection requires a value to satisfy every constituent.
  • Conflicting property types can produce unusable never fields.
  • Inspect the combined shape before composing public contracts.

Type guards

Teach the checker how runtime predicates establish a narrower static type.

  • A type predicate connects a runtime check to static narrowing.
  • Validate the complete condition claimed by the predicate.
  • Unsound guards can make incorrect code appear type-safe.

Literal and primitive types

Model exact strings, numbers, booleans and object shapes instead of broad primitives.

  • Use literal unions for a finite set of valid values.
  • Distinguish wrapper objects from primitive string and number types.
  • Preserve specific values where later narrowing depends on them.

Enums and alternatives

Choose unions or enums based on runtime needs, serialization and API ownership.

  • String unions can model alternatives without generated enum objects.
  • Enums provide named runtime values with their own emit behavior.
  • Consider serialization and library boundaries before choosing.

Function overloads

Describe several supported call signatures while keeping one checked implementation.

  • Expose overload signatures for genuinely different supported calls.
  • Make the implementation compatible with every public signature.
  • Prefer a union parameter when overloads add no useful relationship.

Variance and assignability

Understand when function parameters and generic containers can safely substitute for one another.

  • Assignability depends on how a generic parameter is consumed or produced.
  • Callback parameter safety differs from simple return-value compatibility.
  • Test public generic APIs under strict function checking.

Type manipulation

Utility types

Transform existing types with Partial, Pick, Omit, Record, ReturnType and Awaited.

  • Use Pick and Omit to select object properties.
  • Use Partial or Required to change optionality deliberately.
  • Derive function and promise results with ReturnType and Awaited.

satisfies and as const

Validate configuration while retaining precise literal types.

  • satisfies checks compatibility without discarding useful inferred detail.
  • as const preserves literal values and readonly tuple or object shapes.
  • Neither construct freezes or validates incoming runtime data.

Template literal types

Generate string unions from naming rules and validate event or route keys.

  • Combine literal unions to describe valid string patterns.
  • Use key remapping to create related event or accessor names.
  • Avoid enormous cross-product unions that slow checking.

Conditional and mapped types

Build reusable type transformations that inspect and remap the shape of another type.

  • Conditional types choose results based on assignability.
  • Mapped types transform keys and modifiers of existing shapes.
  • Control distributivity when transforming a union as a whole.

Indexed access types

Derive property and array element types directly from an existing model.

  • Read a property's type with Model['property'].
  • Use an array's number index to obtain its element type.
  • Constrain dynamic keys with keyof the source model.

Infer in conditional types

Extract related types inside reusable conditional transformations.

  • Use infer to capture a matched type inside a conditional branch.
  • Extract function parameters, return values or nested element types.
  • Define what should happen when the source shape does not match.

Configuration

Strict compiler checks

Use strict mode and modern defaults to make invalid states visible at compile time.

  • Enable strictness deliberately and fix meaningful diagnostics.
  • Model null and undefined at actual data boundaries.
  • Avoid suppressing errors through broad assertions or any.

Modules and resolution

Configure Node.js and bundler modules, including TypeScript 7's modern resolution rules.

  • Match module and moduleResolution to the execution environment.
  • Verify package exports and ESM/CommonJS interoperability.
  • Remember compiler path mappings do not rewrite runtime imports.

tsconfig migration

Replace removed or deprecated options and make the compiler target explicit.

  • Audit configuration for deprecated or removed options.
  • Set target, module and type libraries for the actual runtime.
  • Compare effective configuration before and after the upgrade.

noUncheckedIndexedAccess

Make indexed lookups acknowledge that a key may not exist at runtime.

  • Indexed reads can include undefined when a key may be absent.
  • Check lookup results before accessing their properties.
  • Use explicit required properties where existence is guaranteed.

exactOptionalPropertyTypes

Distinguish an omitted optional property from one explicitly assigned undefined.

  • An absent optional key differs from a present undefined value.
  • Include undefined explicitly when assigning it is intentional.
  • Test object spreading and patch payloads at API boundaries.

JavaScript interop

Decorators and classes

Type object-oriented code and standard decorators without weakening the public API.

  • Distinguish standard decorators from legacy decorator semantics.
  • Type constructor, instance and decorator context contracts explicitly.
  • Verify required metadata integrations before switching modes.

Declaration files

Describe untyped JavaScript packages and publish accurate public types for consumers.

  • Describe runtime exports accurately in .d.ts files.
  • Keep ambient declarations separate from implementation code.
  • Test published types against a small consuming project.

Module augmentation

Extend third-party declarations locally when a package's public types need an application-specific addition.

  • Augment the exact module name exported by the package.
  • Add compatible declarations rather than replacing implementation behavior.
  • Ensure the augmentation file is included by the consumer's compiler.

JSDoc checking

Add useful static checking to JavaScript projects without converting every file to TypeScript.

  • Enable checkJs for JavaScript that should receive diagnostics.
  • Annotate parameters and reusable types with supported JSDoc tags.
  • Migrate files gradually while retaining runnable JavaScript.

Migration

Migration from TypeScript 6

Clear deprecations first, then switch compiler versions and verify API-dependent tools.

  • Resolve TypeScript 6 deprecations before adopting the native compiler.
  • Verify dependencies that rely on compiler or language-service APIs.
  • Compare CI diagnostics and emitted artifacts during the transition.

Migrating from any

Replace unchecked escape hatches with unknown, validation and precise domain types.

  • Use unknown for data whose shape is not yet established.
  • Validate at the boundary before assigning a domain type.
  • Remove unsafe any flows incrementally with focused checking.

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