Export Analysis reports wrong sizes

Describe the bug

https://bundlephobia.com/result?p=@timvir/core@0.0.14

The size of the fullWidth and extendedWidth should be a few bytes, not 9kB! If you look at the source (https://unpkg.com/browse/@timvir/core@0.0.14/index.js), the extendedWidth export is essentially this:

function cx(...classNames) {
  return classNames.filter(Boolean).join(' ');
}

const noLayout = "n13r7o41";
export const extendedWidth = cx(noLayout, "ev9kr8h");

To Reproduce

Source and output from bundlephobia available in the links above.

Expected behavior

The size of the fullWidth and extendedWidth exports should be a few bytes. The whole block above is only ~163 bytes (uncompressed).

[pablo-abc]

Upon further inspection I think I found a solution to this. Removing the "browser" property from my package’s package.json, or pointing it to the esm output makes Bundlephobia report the correct sizes now as seen here. The only thing I find weird about this is that package-build-stats correctly pointed the path to my esm output, even if it wasn’t using that one to calculate the sizes?

There’s basically three things required for Bundlephobia to report the correct sizes of each module on its “Export Analysis”:

1. Your exported modules should each be in a separate file
2. Your bundler should preserve said modules in separate files (in rollup this would mean either using multiple entry points, or using output.preserveModules = true).
3. Your package.json should point its "browser" property to your esm bundle, not umd nor cjs.

I’m not sure if this is a bug in Bundlephobia, but webpack does tree shake properly regardless of the "browser" property (as per my previous comment).

[pablo-abc]

I’m having the same issue with some of my packages. This one being a great example since it’s just a bunch of utils. I’m using Rollup to bundle these packages but I have confirmed in a simple project that webpack does tree shake unused imports. This is how I’m testing it:

// webpack.config.js
const path = require('path');

module.exports = {
  entry: './src/index.js',
  output: {
    filename: 'main.js',
    path: path.resolve(__dirname, 'dist'),
  },
  mode: 'development',
  optimization: {
    usedExports: true,
    innerGraph: true,
    sideEffects: true,
  },
  devtool: false,
};

// src/index.js
import { _get } from '@felte/common';

const res = _get({ prop: 'value' }, 'prop');
console.log(res);

// package.json
{
  "main": "index.js",
  "scripts": {
    "build": "webpack"
  },
  "devDependencies": {
    "webpack": "^5.66.0",
    "webpack-cli": "^4.9.1"
  },
  "dependencies": {
    "@felte/common": "0.6.0"
  }
}

The resulting bundle does tree-shake everything but _get. But, unless I’m understanding incorrectly what Bundlephobia’s export analysis does, it’s implying this would bundle 2.3kb instead of the few bytes that the method itself uses.

Note: these are all named exports, exported from a single index.js file.