ESBuild library default export in incorrect format

Question

I have written a library that exports a single object like this

export default class JWTSigner

This works fine in the tests for the library where it is imported like this:

import JWTSigner from '../index';

When consuming the package I import it like this:

import JWTSigner from 'jwt-on-kms';

which does not result in any Typescript errors. When I run esbuild and run the resulting bundle I get this error

{"errorType":"TypeError","errorMessage":"import_jwt_on_kms.default is not a constructor","stack":["TypeError: import_jwt_on_kms.default is not a constructor","    at Object. (/var/src/functions/register.ts:71:43)","    at Module._compile (node:internal/modules/cjs/loader:1105:14)","    at Object.Module._extensions..js (node:internal/modules/cjs/loader:1159:10)","    at Module.load (node:internal/modules/cjs/loader:981:32)","    at Function.Module._load (node:internal/modules/cjs/loader:822:12)","    at Module.require (node:internal/modules/cjs/loader:1005:19)","    at require (node:internal/modules/cjs/helpers:102:18)","    at _tryRequireFile (file:///var/runtime/index.mjs:869:37)","    at _tryRequire (file:///var/runtime/index.mjs:919:25)","    at _loadUserApp (file:///var/runtime/index.mjs:945:22)"]}

And if I log the JWTSinger object at this point I get: { default: [class JWTSigner2] }. If I modify the bundle to use JWTSigner.default.default as the constructor instead it works perfectly. My Question is why is the default export getting wrapped in another object and how can I prevent this?

My build script is:

esbuild.build({
  entryPoints: entryPoints,
  bundle: true,
  outdir: path.join(__dirname, outdir),
  outbase: path.join(__dirname, functionDir),
  platform: 'node',
  external: ['aws-sdk'],
  minify: isProd,
  sourcemap: !isProd,
}).catch(() => process.exit(1))

ESBuild library default export in incorrect format

0 Answers