Typescript: Define type by string

Question

I saw below evaluation in some external sources (that I want to use in my project):

const INIT: 'jsonforms/INIT' = 'jsonforms/INIT'

1. What does this mean (defining type by a string ( INIT: 'jsonforms/INIT' ))? How a string ( 'jsonforms/INIT' ) can be a type?

   What is this called officially?

2. My Webpack complains about this during build and needs additional loader :

    styleTagTransform.js:16 Uncaught Error: Module parse failed: Unexpected token (36:17) File was processed with these loaders: *./node_modules/@pmmmwh/react-refresh-webpack-plugin/loader/index.js *./node_modules/source-map-loader/dist/cjs.js You may need an additional loader to handle the result of these loaders. | import { ErrorTranslator, Translator } from '../i18n'; | > export const INIT: 'jsonforms/INIT' = 'jsonforms/INIT'; | export const UPDATE_CORE: 'jsonforms/UPDATE_CORE' = `jsonforms/UPDATE_CORE`; | export const SET_AJV: 'jsonforms/SET_AJV' = 'jsonforms/SET_AJV';

---

Another complaination is here:

export type CoreActions =
  | InitAction
  | UpdateCoreAction
  | UpdateAction;

What does the above syntax mean?!

Uncaught Error: Module parse failed: Unexpected token (65:7)
File was processed with these loaders:
 * ./node_modules/@pmmmwh/react-refresh-webpack-plugin/loader/index.js
 * ./node_modules/source-map-loader/dist/cjs.js
You may need an additional loader to handle the result of these loaders.
| export const REMOVE_DEFAULT_DATA = `jsonforms/REMOVE_DEFAULT_DATA`;
| 
> export type CoreActions =
|   | InitAction
|   | UpdateCoreAction

Answer 1

How a string ('jsonforms/INIT') can be a type?

In TypeScript, this type is a literal .

 export type CoreActions = | InitAction | UpdateCoreAction | UpdateAction;

What does the above syntax mean?!

This one is an union .