Why __export function handle 「lodash-es/debounce」 module wrap with an additional function

[Ezrealzbb]

Context

This is a npm package A peerDependency with「lodash-es」package；there is inner source code：

// tracker.ts
import { debounce } from 'lodash-es';
class ImageTracker {
  collectResolvedImagesInfoBatchly: any = debounce(this.collectResolvedImagesInfo, 3000);
  collectResolvedImagesInfo() {}
}
export const docImageTracker = new ImageTracker(ImageType.DOC_IMAGE);

// index.ts
import * as packageA from 'A';

function test() {
  console.log(packageA);
}

test();

we use esbuild：./node_modules/.bin/esbuild index.ts --bundle --outfile=out.js

we can find the code in out.js

  // node_modules/lodash-es/debounce.js
  var debounce_exports = {};
  __export(debounce_exports, {
    // notice: there is a function which wraps the debounce_default variable
    default: () => debounce_default // code #1
  });
  function debounce(func, wait, options) {}
  var init_debounce = __esm({
    "node_modules/lodash-es/debounce.js"() {
      init_isObject();
      init_now();
      init_toNumber();
      FUNC_ERROR_TEXT2 = "Expected a function";
      nativeMax = Math.max;
      nativeMin = Math.min;
      debounce_default = debounce;
    }
  });

// node_modules/A.umd.js
var require_sheet_common_umd = __commonJS({
    "node_modules/A.umd.js"(exports2, module2) {  (init_debounce(), debounce_exports)

Object.defineProperty(t2, "__esModule", { value: true }), t2.driveImageTracker = t2.docImageTracker = void 0;
          var r2, o2, i2, a2 = n2(156), c2 = (r2 = a2) && r2.__esModule ? r2 : { default: r2 }, u2 = n2(0);
 // source code had been transformed as
  this.collectResolvedImagesInfoBatchly = (0, c2.default)(this.collectResolvedImagesInfo, 3e3) // code #2

 }

package A is an umd bundle by webpack4。the out.js can be upload together in this issue；

problem：

the value of c2 in runtime is { default: { default: funtion debounce } }；code #2 throw an error ：(0 , c2.default) is not a function;

question

1. why code#1 use another function wrap debounce_default?
2. Could lodash-es/debounce module definition add an __esModule flag in code#1?

expected

the value of c2 in runtime to be { default: funtion debounce() {} }。or __export code#1 width __esModule

Thanks ~

outjs.zip

[Ezrealzbb]

I use package alias："lodash-es": "npm:lodash@4.17.21", in package.json，it's works。but why?

[evanw]

why code#1 use another function wrap debounce_default?

I'm not sure I understand what you're saying. But __export exists to make sure the export is read-only (as required by the JavaScript specification) and the __esm wrapper exists to allow that module to be lazily-evaluated. You haven't posted enough code to be able to understand why this lazy evaluation is needed but it's likely because that module was imported using require() instead of import, which means the import happens at run-time instead of at compile-time. In that case lazy evaluation is needed.

2. Could lodash-es/debounce module definition add an __esModule flag in code#1?

What version of esbuild are you using? Any chance this has already been fixed by #1338? The __esModule flag has already been added in version 0.12.7 of esbuild.

[Ezrealzbb]

Thank for your reply.

You haven't posted enough code to be able to understand why this lazy evaluation is needed but it's likely because that module was imported using require() instead of import

source code is very simple. debounce module imported by import syntax；

// tracker.ts  is an es module
import { debounce } from 'lodash-es';
class ImageTracker {
  collectResolvedImagesInfoBatchly: any = debounce(this.collectResolvedImagesInfo, 3000);
  collectResolvedImagesInfo() {}
}
export const docImageTracker = new ImageTracker(ImageType.DOC_IMAGE);

which means the import happens at run-time instead of at compile-time. In that case lazy evaluation is needed.

Your words remind me that peerDeependcy will not package lodash-es into a product bundle directly. May I think like this: The output umd bundle loads lodash-es/debounce by require() syntax and then esbuild recognizes lodash-es/debounce as a cjs require，uses __export to load code？

What version of esbuild are you using? Any chance this has already been fixed by #1338? The __esModule flag has already been added in version 0.12.7 of esbuild.

My esbuild version is 0.12.16. The issue of #1338 is same to me, but it has no __esModel flag in output code. cc @lbwa

[lbwa]

As evan said, we need enough code to figure out what's going on. Please provide a complete and minimal reproduce repo, instead of code snippets.

[Ezrealzbb]

As evan said, we need enough code to figure out what's going on. Please provide a complete and minimal reproduce repo, instead of code snippets.

Sorry I cant provide a complete code becouse it used private npm package within the company. But I check the esbuild version again. it's throw problem with 0.11.5. It works when upgrading to 0.12.16.thanks.

there is no question and the issue can be closed.