Error: 'default' is not exported

[fryorcraken]

This seems to be a common error but I am not able to understand how to resolve it.

The code is here: https://github.com/waku-org/js-rln/tree/18176e33c06c35a78af25b512f7615617c2c0775

I am getting

[!] Error: 'default' is not exported by dist/witness_calculator.cjs, imported by dist/witness_calculator.js
https://rollupjs.org/guide/en/#error-name-is-not-exported-by-module
dist/witness_calculator.js (1:7)
1: import builder from './witness_calculator.cjs';
          ^
2: export { builder };
3: //# sourceMappingURL=witness_calculator.js.map

So builder is exported as default.

in dist/witness_calculator.cjs:

module.exports = async function builder(code, options) {

in dist/witness_calculator.js:

import builder from './witness_calculator.cjs';
export { builder };

My rollup config:

import { nodeResolve } from "@rollup/plugin-node-resolve";
import commonjs from "@rollup/plugin-commonjs";
import json from "@rollup/plugin-json";
import { wasm } from '@rollup/plugin-wasm';

export default {
  input: {
    index: "dist/index.js"
  },
  output: {
    dir: "bundle",
    format: "esm",
  },
  plugins: [
    commonjs(),
    json(),
    nodeResolve({
      browser: true,
      preferBuiltins: false,
    }),
    wasm({targetEnv: "browser"})
  ],
};

I am not sure to understand why rollup does not find the default export?

[potatohoney-p]

In the linked revision, the important part is the end of the emitted dist/witness_calculator.cjs, not just its module.exports line.

I reproduced this with the versions from that revision's lockfile: TypeScript 4.8.2, Rollup 2.79.0, and @rollup/plugin-commonjs 22.0.2. Running the original src/witness_calculator.cjs through TypeScript with allowJs: true and module: "es2020" adds this at the end:

export {};

The output now mixes CommonJS assignment with ES-module syntax. Bundling the wrapper with commonjs() then produces the same MISSING_EXPORT error in your question. transformMixedEsModules: true alone also still fails in this reproduction; it doesn't turn that empty ESM export into the missing default export.

A small fix for this generated file is to preserve its original CommonJS contents when staging dist, rather than feeding the TypeScript-rewritten copy to Rollup. For example, after tsc and before Rollup:

node -e "require('node:fs').copyFileSync('src/witness_calculator.cjs', 'dist/witness_calculator.cjs')"

Then leave the wrapper as:

import builder from './witness_calculator.cjs';
export { builder };

In the isolated reproduction, that one replacement makes the bundle succeed without warnings; importing the resulting ESM bundle exposes builder as a function. No CommonJS plugin option change was needed. For a permanent build pipeline, treat the generated CJS as a copied asset (and make sure a later/watch tsc run doesn't overwrite it again). If you retain sourcemaps, don't ship a stale map for the replaced file.

The CommonJS plugin already explicitly handles .cjs files in v22.0.2, so adding .cjs to extensions is not the missing piece here. The original TypeScript configuration is what makes inspecting the emitted file important.

This verifies the reported export/bundling failure using the original calculator source, not the entire RLN application or execution of its WASM circuit.