TypeScript - terser is not callable

[RobertSandiford]

The sample code for @rollup/plugin-terser is not working for me

The error can be seen on TS Playground here:

https://www.typescriptlang.org/play?target=99&moduleResolution=99&module=199&declaration=false&esModuleInterop=false&jsx=1#code/JYWwDg9gTgLgBDAplAzsuAzKERwOQAC2ANsQK5gD0Y5A5sAHYC0SqyeA3ALABQviAD0iw4AE0QYAhmWLwA3rzhxGYMjABc+FFADGlRuIEA6AFYo8AGkVwIa1RrgKeSpaOBRNeWzHuXrSjGgQSQc8HTM8awBfK2c4GjJ6BhRNAG1WNCgACgBKAF1eKI4gA

Settings can be viewed on TS playground, generally modern environment e.g. module and module resolution: NodeNext

[RobertSandiford]

Sorry TS playground is being buggy. Go to TS Config -> Target and set it to ES2022. Then the error appears.

[potatohoney-p]

I reproduced TS2349 locally with an ESM config (config.mts), module/moduleResolution: "NodeNext", target: "ES2022", TypeScript 5.2.2 and @rollup/plugin-terser 0.4.4. The same check also fails with TypeScript 5.9.3, including with esModuleInterop: true. I also checked the current plugin 1.0.2 with TS 5.9.3: the ESM type-check still fails.

The relevant detail is the package's declaration entry: it points both import modes at types/index.d.ts, which has export default function terser(...), but its enclosing package has no "type": "module". Under NodeNext, TypeScript therefore interprets that declaration as CommonJS. The runtime ESM entry and the declaration's module format don't line up. TypeScript's module-format rules explain why the consuming file's format matters here.

Two config-level workarounds I verified with plugin 0.4.4 / Rollup 3.29.0:

• Use a plain rollup.config.mjs with the documented import terser from '@rollup/plugin-terser'. rollup -c rollup.config.mjs successfully minified a small fixture. This avoids this TypeScript config check; it does not fix the declarations or preserve TS checking for the config.
• If a CommonJS config is acceptable, put the same import/config in rollup.config.cts, compile it to .cjs, then run that emitted config:

tsc rollup.config.cts --module NodeNext --moduleResolution NodeNext --target ES2022 --esModuleInterop false --skipLibCheck --outDir .config-build
rollup -c .config-build/rollup.config.cjs

The .cts version type-checked with both TS versions above, and its emitted config successfully minified the fixture; the generated module returned the expected value at runtime. skipLibCheck alone does not suppress TS2349 in the .mts consumer.

I would avoid replacing the call with terser.default() just to satisfy this type view: that changes the runtime access, whereas the actual ESM export is already the callable function. These tests cover a minimal local config, not the Playground's dependency-loading implementation.