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--allowImportingTsExtensions lets TypeScript imports include source extensions such as .ts, .mts, and .tsx. In a monorepo, it can support source-level imports when a bundler or TypeScript-capable runtime resolves those files. It does not link workspace packages or make emitted JavaScript able to load a .ts file. The option dates to TypeScript 5.0; it is useful in a TypeScript 6.0-era setup, but it was not introduced in 6.0.
What the option unlocks—and what it does not
Normally, TypeScript expects import specifiers to be meaningful to the eventual runtime or build output. The flag permits TypeScript source imports to name files with TypeScript-specific extensions, for example:
import { formatDate } from "./formatDate.ts";This can be convenient when the tool consuming the code works directly with TypeScript source, such as a bundler that transpiles it or a runtime/loader that executes or transpiles TypeScript. TypeScript lists Node, Deno, and Bun as direct TypeScript runtime examples, and ts-node and tsx as transpiling loaders. The flag itself only changes what TypeScript permits; the host tool must still understand and resolve the import. See TypeScript’s option reference and its module theory guide.
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- It does not select the runtime’s resolver rules.
- By itself, it does not turn a
.tsimport into a path that works in emitted JavaScript.
Why the emit constraint matters
TypeScript documents allowImportingTsExtensions for projects using noEmit or emitDeclarationOnly. In those modes, TypeScript is not producing JavaScript that would retain a source import such as ./formatDate.ts and then fail to find that file at runtime. A bundler or TypeScript runtime handles the source instead.
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If your build emits JavaScript, enabling the flag alone is not enough. TypeScript 5.7 added rewriteRelativeImportExtensions, which rewrites relative .ts, .tsx, .mts, or .cts specifiers to their JavaScript equivalents in output. Check the exact supported combination and defaults for the compiler version you install; the TypeScript module theory documentation explains why output-compatible extensions matter.
Choose a setup based on who resolves the imports
Before enabling the option, identify whether your project checks TypeScript without emitting JavaScript, or emits JavaScript for a runtime to execute. Then match moduleResolution to the actual host. TypeScript documents bundler for bundlers and Bun; do not assume that a flag or resolution mode makes Node, a bundler, and other runtimes interchangeable.
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| Setup | What handles the source import | Configuration consideration |
|---|---|---|
| No-emit check with a bundler | The bundler resolves and transpiles TypeScript source. | Use a resolver mode that models the bundler; bundler is the documented choice for bundlers. |
| Direct TypeScript runtime or loader | The runtime or loader resolves and executes or transpiles TypeScript. | Confirm that the chosen host supports the import form and configure TypeScript resolution to match it. |
| JavaScript-emitting build | The generated JavaScript is resolved by its eventual runtime. | Use output-compatible specifiers or verify extension rewriting, including rewriteRelativeImportExtensions, for the installed compiler. |
The table describes responsibilities, not a guarantee that every tool accepts every configuration. Verify the host’s behavior as well as TypeScript’s checks.
Use workspaces for imports between monorepo packages
There are two different kinds of import to plan for: a relative import within one package, and an import from one package to another. The flag concerns TypeScript-extension specifiers; it does not replace package management for the second case.
For sibling packages, use npm, Yarn, or pnpm workspaces so the packages are linked into node_modules and resolved as packages. Import across the package boundary by its package name, with the package’s metadata participating in resolution. TypeScript’s ESM and Node.js guidance explains workspace-based package resolution.
A paths alias that points directly at another package’s source may be useful for some internal workflows, but it can bypass the package metadata and resolution path that consumers will use. If a package is intended for publication—or you want the monorepo to test its real package boundary—prefer workspace linking and package-name imports. Keep that choice separate from whether relative imports inside a package use .ts extensions.
Is this a TypeScript 6.0 feature?
No. The TSConfig reference identifies allowImportingTsExtensions as released in TypeScript 5.0. TypeScript 6.0 is relevant as the compiler context for 2026, not as the origin of this option. The TypeScript 6.0 release notes describe 6.0 as a transition release toward TypeScript 7.0 and cover other module changes.
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