compiler crashes with allowJs and dynamic import

[MirKml]

TypeScript Version: 3.1.3 2.9.2

Code
tsjs-crash.zip

Minimal example is in the attached zip package. Extract it somewhere, go to main directory with tsconfig.json and

install
npm i
compile
node node_modules/typescript/bin/tsc

Expected behavior:
everything works fine - preferred, because with TS 2.8.x there are no errors,
or some reasonable error message for problem solving

Actual behavior:
compiler crashes with

 E:\projects\vscode-crash\node_modules\typescript\lib\tsc.js:69365
                throw e;
                ^
TypeError: Cannot read property 'parent' of undefined
    at Object.getDeclarationOfExpando (E:\projects\vscode-crash\node_modules\typescript\lib\tsc.js:7328:19)
    at getTypeOfFuncClassEnumModule (E:\projects\vscode-crash\node_modules\typescript\lib\tsc.js:28883:40)
    at getTypeOfSymbol (E:\projects\vscode-crash\node_modules\typescript\lib\tsc.js:28984:24)
    at checkImportCallExpression (E:\projects\vscode-crash\node_modules\typescript\lib\tsc.js:40833:96)
    at checkExpressionWorker (E:\projects\vscode-crash\node_modules\typescript\lib\tsc.js:42356:32)
    at checkExpression (E:\projects\vscode-crash\node_modules\typescript\lib\tsc.js:42301:42)
    at checkAwaitExpression (E:\projects\vscode-crash\node_modules\typescript\lib\tsc.js:41525:31)
    at checkExpressionWorker (E:\projects\vscode-crash\node_modules\typescript\lib\tsc.js:42383:28)
    at checkExpression (E:\projects\vscode-crash\node_modules\typescript\lib\tsc.js:42301:42)
    at checkExpressionCached (E:\projects\vscode-crash\node_modules\typescript\lib\tsc.js:42182:38)

Problem is with the imported javascript in TestComponent.tsx with

async exportToXlsx(exportSelected: boolean = false) {
    const xlsx = await import('./js-xlsx/xlsx');
}

Problem is only with Typescript 2.9, 3.x, Typescript 2.8 compiles without any errors.

I tried to exclude javascript with tsconfig.json and jsconfig.json - see exclude properties in these files, but nothing works. Javascript is always compiled. So another question - is it possible exclude javascripts in similar situations?

[sandersn]

The immediate cause is the improved handling of module.exports in Typescript 2.9. The compiler is trying to figure out what the exports of ./js-xlsx/xlsx are, but somehow creates a defective export= symbol from the line module.exports = CFB.

Workaround

Any time you import a file, the compiler will read that file. Excludes will not help you. For a JS file that you do not want to compile, but nonetheless want to import, the easiest workaround is to put a d.ts file next to it. Here's the one I created:

// @Filename: components/js-xlsx/xlsx.d.ts
declare var dummy: any;
export = dummy;

This just exports a dummy variable with the type any so that the compiler doesn't spend any time analysing xlsx.js to figure out what it actually exports.

Edit: You are free to make the type of dummy as accurate as you want; it will probably be more accurate than the type the compiler produces after this bug is fixed.

[sandersn]

Here's a small repro:

// @Filename: mod1.js
exports.version = 1
module.exports = NotDefined
// @Filename: test.js
import('./test')

[MirKml]

Thank you for analysis and workaround. I will try it.

I found another possible workaround. I made another node_modules directory and copy the whole directory js-xlsx inside it. So the directory tree is components/node_modules/js-xlsx`/xlsx.js.
Dynamic import will be import('js-xlsx/xlsx).

It seems that because of module resolution or something like that, the compiler ignores the node_modules even of dynamic import. Final app is build via webpack and babel and it seems it has no problem with it.
What do you think about that?

I definitely waiting for the final typescript fix, thank you.

[sandersn]

Duplicating part of the source tree seems hackier than dropping a d.ts in beside the .js file.

Anyway, the fix is simple so it should be in typescript@next in the next day or two.