How to import shared typescript code using create-react-app (no eject)?

You could use craco (create-react-app config override) to override the webpack config (abstracted as part of CRA) without ejecting.
Additionally you could use ts-loader to reference non-transpiled ts code directly in external projects (e.g. if you wanted to reference/use shared code/lib as part of a mono-repo).

Assuming your CRA app is in the client directory your project structure is like the following:

client/
|--src/
|--package.json
shared/
|--package.json
|--(ts files)
package.json

cd client
yarn add -D @craco/craco ts-loader

2. create a craco.config.js file in the client/ (CRA) directory
3. ensure the craco.config.js has the following content

const path = require("path");

module.exports = {
  webpack: {
    configure: webpackConfig => {

      // ts-loader is required to reference external typescript projects/files (non-transpiled)
      webpackConfig.module.rules.push({
        test: /\.tsx?$/,
        loader: 'ts-loader',
        exclude: /node_modules/,
        options: {
          transpileOnly: true,
          configFile: 'tsconfig.json',
        },
      })
      
      return webpackConfig;
    }
  }
};

4. Replace react-scripts commands in client/package.json with craco

/* client/package.json */

"scripts": {
-   "start": "react-scripts start",
+   "start": "craco start",
-   "build": "react-scripts build",
+   "build": "craco build"
-   "test": "react-scripts test",
+   "test": "craco test"
}

UPDATE: Since react-app-rewired is only maintained passively and doesn't support CRA versions 2+ (we are are three major versions later at the time of writing), I would no longer recommend this approach.

After more hours of experimenting and reading up on GitHub issues, I finally have a working solution. Big thanks to BirukDmitry who made this very helpful post on GitHub. Step-by-step guide:

1. Install react-app-rewired and customize-cra

    npm i react-app-rewired customize-cra --save-dev
   

2. Configure react-app-rewird with a minimal config-overrides.js like this:

   const { removeModuleScopePlugin, override, babelInclude } = require("customize-cra");
   const path = require("path");
   
   module.exports = override(
     removeModuleScopePlugin(),        // (1)
     babelInclude([
       path.resolve("src"),
       path.resolve("../common/src"),  // (2)
     ])
   );
   

   Setting (1) is similar to what is needed for getting around the import-outside-src limitation in general (see linked question).

   Setting (2) is crucial though to enabled babel-transpilation (and thus, including TS type stripping I presume) for other paths as well. This is where you have to put add your paths from which you want to import.

3. No adaptations needed for tsconfig.json.

4. Import using relative paths, e.g., import * as mymodule from '../../common/src/mymodule'.

The alias solution for craco or rewired create-react-app is react-app-alias for systems as: craco, react-app-rewired, customize-cra

According docs of mentioned systems replace react-scripts in package.json and configure next:

react-app-rewired

// config-overrides.js
const {aliasWebpack, aliasJest} = require('react-app-alias')

const options = {} // default is empty for most cases

module.exports = aliasWebpack(options)
module.exports.jest = aliasJest(options)

craco

// craco.config.js
const {CracoAliasPlugin} = require('react-app-alias')

module.exports = {
  plugins: [
    {
      plugin: CracoAliasPlugin,
      options: {}
    }
  ]
}

all

Configure aliases in json like this:

// tsconfig.paths.json
{
  "compilerOptions": {
    "baseUrl": ".",
    "paths": {
      "example/*": ["example/src/*"],
      "@library/*": ["library/src/*"]
    }
  }
}

And add this file in extends section of main typescript config file:

// tsconfig.json
{
  "extends": "./tsconfig.paths.json",
  // ...
}

@bluenote10 solution did the trick!

There was only one issue in step #2 that prevents Babel from transpilling ts files from ../../common/src That is modified version of @bluenote10's code (that finally worked for me)

1. Install react-app-rewired and customize-cra

    npm i react-app-rewired customize-cra --save-dev
   

2. Configure react-app-rewird with a minimal config-overrides.js like this:

    const { removeModuleScopePlugin, override, babelInclude } = require("customize-cra");
    const path = require("path");
   
    module.exports = function (config, env) {
   
        return Object.assign( // We need Object.assign() to not to loose initial config 
          config,
          override(
            removeModuleScopePlugin(),       //1
            babelInclude([
              path.resolve('src'),
              path.resolve('../common/src'), //2
            ])
          )(config, env)
        )
      }
   
   

   Setting (1) is similar to what is needed for getting around the import-outside-src limitation in general (see linked question).

   Setting (2) is crucial though to enabled babel-transpilation (and thus, including TS type stripping I presume) for other paths as well. This is where you have to put add your paths from which you want to import.

3. No adaptations needed for tsconfig.json.

4. Import using relative paths, e.g., import * as mymodule from '../../common/src/mymodule'.

question where does ../../common/src/mymodule lives at ? is it another project ? If it is another project why dont you link'em

• inside common code project run npm link

• inside the project that will use the common code: npm link common-project

If there are not two different projects. why does it has to be outside of src ?

The link you posted The create-react-app imports restriction outside of src directory and your case/problem are two totally different thing, plus they be tripping so hard. let me give you and idea of that problem and yours.

As we already know CRA creates a SPA single page app. which means that there is only one single html file. everything happens at the index.html which is located at <project>/public/index.html. If we compile the code we'll notice something the end bundle might look some like this

build
--static
----js
----css
----media
--index.html
--...more hashed crap...
public
src

and by default process.env.PUBLIC_URL is set to "/" WHAT?? yes look let me show you. there is an old say a picture explains more than 1000 words.

if we look at the image that according to its path it is located at ./src/styles/imageSlack.jpg or some. So what if we console.log it.

WHAAAT!! where they do that at ? one thing you can do to test my theory is if you console.log(process.env.PUBLIC_URL) any where in yow code. now here is the big diference between this and that.

Browsers natively do not know Typescript.

So either you set yow code inside src and we end happy or follow the separate of concerns principle and we create an npm package with the shared code and just imported as any other module.