"(void 0) is not a constructor" when trying to access esbuild minified class

Question

I've got a class defined in an npm package:

export default class SomeClass{
    constructor({ testA, testB }) {
        this.testA = testA;
        this.testB = testB;
    }

    log() {
        console.log(this.testA + this.testB);
    }
}

That then gets aggregated with another file in the source file:

import SomeClass from './some-class';
import anotherFunction from './another-function';

export { SomeClass, anotherFunction };

And then built with the esbuild config as below:

const esbuild = require('esbuild');

async function bundle() {
    await esbuild.build({
      logLevel: 'info',
      entryPoints: ['src/js/package.js'],
      bundle: true,
      minify: true,
      sourcemap: true,
      outfile: 'dist/js/package.min.js'
    })
      .catch(() => process.exit(1));
  }

bundle();

But when I try import that into my app's app.js as such:

import { SomeClass } from '../package.min.js';
const newClass = new SomeClass(constructorObject);

I get the aforementioned void 0 message.

If I open the minified js file I do see a message about the class not being referenced anywhere else, is there something I can do to make it export the file?

Answer 1

Thanks @Bergi for pointing me in the right direction. The solution was adding

format: 'esm'

to my esbuild script options. Though for projects importing libraries in the CJS format the value cjs could presumably be placed there instead.

The full build function now looks like:

async function bundle() {
    await esbuild.build({
      logLevel: 'info',
      entryPoints: ['src/js/employee-portal-assets.js'],
      bundle: true,
      minify: true,
      sourcemap: true,
      treeShaking: true,
      format: 'esm',
      outfile: 'dist/js/employee-portal-assets.min.js'
    })
      .catch(() => process.exit(1));
  }