Named import umd module returns null when the module uses the export let syntax

[anyesu]

Describe the bug

I used the vue-amap library in my project. I found that when I imported it using import { lazyAMapApiLoaderInstance } from 'vue-amap' , the value of lazyAMapApiLoaderInstance was always null instead of the latest value.

The source code of lazyAMapApiLoaderInstance uses the export let syntax to delay initialization:

let lazyAMapApiLoaderInstance = null;
import AMapAPILoader from './lazy-amap-api-loader';
import Vue from 'vue';
export const initAMapApiLoader = (config) => {
  if (Vue.prototype.$isServer) return;
  // if (lazyAMapApiLoaderInstance) throw new Error('You has already initial your lazyAMapApiLoaderInstance, just import it');
  if (lazyAMapApiLoaderInstance) return;
  if (!lazyAMapApiLoaderInstance) lazyAMapApiLoaderInstance = new AMapAPILoader(config);
  lazyAMapApiLoaderInstance.load();
};
export { lazyAMapApiLoaderInstance };

ref: https://stackoverflow.com/a/32558929

Reproduction

https://stackblitz.com/edit/vitejs-vite-tdtcgx?file=src%2Fmain.js

Steps to reproduce

pnpm i
# run with Vite
pnpm run dev
# run with Vue CLI
pnpm run dev:vue-cli

Use Vite and Vue CLI to start the project respectively. You can see from the log that the result in Vite is null , while the result in Vue CLI is the expected object .

Then build and run in production mode :

pnpm run build && pnpm run preview

pnpm run build:vue-cli && pnpm run preview

You can see that the behavior in production mode is the same as running in Vue CLI .

The source code after Vite transform is as follows:

import __vite__cjsImport0_vueAmap from "/node_modules/.vite/deps/vue-amap.js?v=7da0ea0b"; const initAMapApiLoader = __vite__cjsImport0_vueAmap["initAMapApiLoader"]; const lazyAMapApiLoaderInstance = __vite__cjsImport0_vueAmap["lazyAMapApiLoaderInstance"];
initAMapApiLoader();
console.log(
  process.env.VITE_APP ? 'vite' : 'vue-cli',
  lazyAMapApiLoaderInstance
);

However, the source code after Webpack transform is as follows:

__webpack_require__.r(__webpack_exports__);
/* harmony import */ var vue_amap__WEBPACK_IMPORTED_MODULE_0__ = __webpack_require__(/*! vue-amap */ "./node_modules/.pnpm/[email protected]/node_modules/vue-amap/dist/index.js");
/* harmony import */ var vue_amap__WEBPACK_IMPORTED_MODULE_0___default = /*#__PURE__*/__webpack_require__.n(vue_amap__WEBPACK_IMPORTED_MODULE_0__);

Object(vue_amap__WEBPACK_IMPORTED_MODULE_0__["initAMapApiLoader"])();
console.log(
  Object({"NODE_ENV":"development","BASE_URL":"/"}).VITE_APP ? 'vite' : 'vue-cli',
  vue_amap__WEBPACK_IMPORTED_MODULE_0__["lazyAMapApiLoaderInstance"]
);

The difference is that Webpack will convert lazyAMapApiLoaderInstance to vue_amap__WEBPACK_IMPORTED_MODULE_0__["lazyAMapApiLoaderInstance"] , while Vite simply defines a local variable to take the value, so console.log cannot read the latest value.

So I think the behavior of Vite should be consistent with Webpack, at least the development mode and production mode should be consistent in Vite.

There are two ways to solve this problem:

• Rename variable bindings like Webpack .

  If simply use RegExp to replace them, it may affect other comments, strings, and local variables with the same name.

  If AST is introduced for parsing, things may become much more complicated. I'm not familiar with AST either.

• This should be documented, in this case the namespace import should be used instead of the named import as shown below. Also throwing warning in transformCjsImport .

  vite/packages/vite/src/node/plugins/importAnalysis.ts

  Line 1002 in c796959

  lines.push(`const ${localName} = ${cjsModuleName}["${importedName}"]`)

  import * as VueAMap from 'vue-amap';
  VueAMap.initAMapApiLoader();
  console.log(
    process.env.VITE_APP ? 'vite' : 'vue-cli',
    VueAMap.lazyAMapApiLoaderInstance
  );

System Info

System:
    OS: Windows 10 10.0.19045
    CPU: (16) x64 11th Gen Intel(R) Core(TM) i7-11700 @ 2.50GHz
    Memory: 26.00 GB / 47.81 GB
  Binaries:
    Node: 16.20.2 - ~\AppData\Local\pnpm\node.EXE
    Yarn: 1.22.18 - D:\software\nodejs\node_global\yarn.CMD
    npm: 8.19.4 - ~\AppData\Local\pnpm\npm.CMD
    pnpm: 8.6.12 - ~\AppData\Local\pnpm\pnpm.EXE
  Browsers:
    Edge: Spartan (44.19041.1266.0), Chromium (116.0.1938.69)
    Internet Explorer: 11.0.19041.1566

Used Package Manager

pnpm

Logs

No response

Validations

• Follow our Code of Conduct
• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• Make sure this is a Vite issue and not a framework-specific issue. For example, if it's a Vue SFC related bug, it should likely be reported to vuejs/core instead.
• Check that this is a concrete bug. For Q&A open a GitHub Discussion or join our Discord Chat Server.
• The provided reproduction is a minimal reproducible example of the bug.

[stackblitz]

Start a new pull request in StackBlitz Codeflow.

• vitejs-vite-tdtcgx (Open reproduction)

[bluwy]

This is hard to fix. We're only rewriting to const initAMapApiLoader = __vite__cjsImport0_vueAmap["initAMapApiLoader"] because vue-amap does not export ESM, so we have to access the APIs through the default import after prebundling. Rewriting it for each referenced variables in code instead would be expensive, but not impossible since we're already doing it for SSR.

[anyesu]

Waiting for you to have a better solution to fix this. I'm currently using this workaround since this case is used less in my projects.

import * as VueAMap from 'vue-amap';
VueAMap.initAMapApiLoader();
console.log(VueAMap.lazyAMapApiLoaderInstance);