Plugin import in angular project throws error 'no default export'

[BingeCode]

Describe the bug
Plugin import throws error in angular project / browser
dayjs__WEBPACK_IMPORTED_MODULE_5__(...).month(...).startOf(...).weekday is not a function

Expected behavior
I can use most dayjs functions just fine with import * as dayjs from 'dayjs'.

But when I need to use plugins, I import with import * as weekday from 'dayjs/plugin/weekday, it throws me this error in the browser - even though the compiler recognises the function weekday just fine:

dayjs__WEBPACK_IMPORTED_MODULE_5__(...).month(...).startOf(...).weekday is not a function

Trying to import the weekday plugin with import weekday from 'dayjs/plugin/weekday'; throws compiler error Module '"C:/.../node_modules/dayjs/plugin/weekday"' has no default export.

OR import { weekday } from 'dayjs/plugin/weekday'; throws compiler error Module '"C:/.../node_modules/dayjs/plugin/weekday"' has no exported member

Information

• Day.js Version 1.8.14
• OS: Win 10 / Angular Typescript Project
• Browser Chrome 74

[iamkun]

Please provide a test repo.

[thomascsd]

Use dayjs.extend, see doc

import * as dayjs from 'dayjs';
import * as weekday from 'dayjs/plugin/weekday';
dayjs.extend(weekday);

[JustFly1984]

Ok, here is the thing, we have same or equal issues with gatsby.js, which is related to:
https://github.com/gatsbyjs/gatsby/blob/master/packages/gatsby-plugin-typescript/README.md

Which is described as:
This plugin uses babel-plugin-transform-typescript to transpile TypeScript. It does not do type checking. Also since the TypeScript compiler is not involved, the following applies:

Does not support namespaces. Workaround: Move to using file exports, or migrate to using the module { } syntax instead.

Does not support const enums because those require type information to compile. Workaround: Remove the const, which makes it available at runtime.

Does not support export = and import =, because those cannot be compiled to ES.next. Workaround: Convert to using export default and export const, and import x, {y} from "z".

https://babeljs.io/docs/en/babel-plugin-transform-typescript.html

[JustFly1984]

the only workaround which works, is to setup tsconfig with

    "esModuleInterop": true,
    "allowSyntheticDefaultImports": true,

[iamkun]

https://day.js.org/docs/en/installation/typescript this might help

[iamkun]

I'll close this issue since it's been a while since it's been opened. Feel free to reopen if you have updates on this