Import from subfolder of npm package

Question

I've been working on creating a small library of React components for use in several other projects. I am publishing the package internally (using a private GitHub repository) and then including in another project. However, when I go to import from a subdirectory of the package I am not able to do so as the paths don't match.

The projects using the package all utilize webpack to bundle/transpile code as I am trying to avoid doing any building in the component library if possible.

Directory Structure

- package.json
- src/
  - index.js
  - Button/
    - index.js
    - Button.jsx
    - ButtonGroup.jsx
  - Header/
    - index.js
    - Header.jsx (default export)

package.json

...
"main": "./src/index.js",
"scripts": "",
...

src/Button/index.js

import Button from './Button';
import ButtonGroup from './ButtonGroup';

export default Button;

export { Button, ButtonGroup};

src/index.js

Is this file actually necessary if only importing from subdirectories?

import Button from './Button';
import ButtonGroup from './Button/ButtonGroup';
import Header from './Header';

export { Button, ButtonGroup, Header };

Other Project

// This project is responsible for building/transpiling after importing
import { Button, ButtonGroup } from 'components-library/Button';

Example

Material-UI is a library of React components that is used by requiring in the following fashion: import { RadioButtonGroup } from 'material-ui/RadioButton. I've tried to figure out how this works for them but to no avail yet.

Similar Questions

• How would I import a module within an npm package subfolder with webpack?
  • This is very nearly the correct approach I require, except that the import path used there involved the src/ directory, which I am trying to avoid (should be component-library/item, not component-library/src/item (which does work currently though))
• Publishing Flat NPM Packages
  • This is exactly what I want except that I was hoping to not have a "build" phase in the package (rely on importing locations to build/transpile)

Questions

1. Can I skip the src/ directory somehow in the import path?
2. Can I skip any type of build phase in the package (so developers don't have to build before committing)?
3. How does a package similar to material-ui handle this?

Solution 1

One of the possible solutions there is webpack aliasing system.
You can create another project, call it for example 'app-aliases', so your aliases will be reusable.
This project will has one js file with all of your packages paths:

const path = require('path');

module.exports = {
'@components': path.resolve(__dirname, 'node_modules/components-library/src'),
'@another': path.resolve(__dirname, 'node_modules/any/path/you/want'),
}

And then add it to the webpack configuration in any project which will be responsible for building/transpiling:
webpack.config.js

const appAliases = require('app-aliases');

const config = {
...
  resolve: {
    alias: {
      ...appAlises
    }
  }
}

In the runtime code you will be able to use it like this:

import {Button} from '@components/Button';
import {Something} from '@another'

If you are using typescript you will need to add the same aliases to the paths tsconfig property.
So answers to your questions are:

1. Yes, you can use any path in aliases
2. Yes, it is not necessary to build all of your projects
3. I see that now mui uses imports from directi packages (core for example), see https://material-ui.com/components/radio-buttons/ there is import Radio from '@material-ui/core/Radio';. But I hope they using re-export that I described below.

Also about node.js resolution mechanism.
When you import some library it tries to find node_modules/some-library/package.json and then main property inside it. This property should lead to your main entry point. Usually it is src/index.js (you should set it in package.json if it is no there yet). In this file you can re-export anything you want from internals file structure and will be able to use it without the full path. Please see this repo for some examples.

Solution 2

Can I skip the src/ directory somehow in the import path?

Yes. Using the package.json "exports" field, which should be supported by Webpack in a near future (see this issue), but has already been supported by Node since Node 12 LTS following the Bare Module Specifier Resolution proposal:

package.json

...
"main": "./src/index.js",
"type": "module",
...
"exports": {
  "./Button": "./src/Button/index.js",
  "./Header": "./src/Header/index.js"
},
...

Now, the following code:

// This project is responsible for building/transpiling after importing
import { Button, ButtonGroup } from 'components-library/Button';

should be translated to:

import { Button, ButtonGroup } from 'components-library/src/Button/index.js';

which should correctly import the requested modules.

Caveat

Now, it would certainly be tempting to try a simpler version like:

...
"exports": {
  "./Button": "./src/Button/",
  "./Header": "./src/Header/"
},
...

so as the usual import statement

import { ... } from 'components-library/Button';

gets translated to

import { ... } from 'components-library/src/Button';

This looks nice, but it will not work in this case, because your submodules don't have each their own package.json file but rely on their index.js file to be found.

/!\ Unlike in CommonJS, there is no automatic searching for index.js or index.mjs or for file extensions.

---

src/index.js - Is this file actually necessary if only importing from subdirectories?

I don't think so, but you can keep it if you want.

---

Can I skip any type of build phase in the package?

Using the "exports" field does not require you to transpile your code.

Solution 3

The answer may depend on how you installed your components library. If you did it via either npm install <git-host>:<git-user>/<repo-name> or npm install <git repo url>,

1. You should be able to import {Button} from 'component-library/Button' as is, according to your first linked question. Similar to Node's require() resolution, Webpack should resolve subdirectories within component-library relative to component-library's entry point. You can find the docs on customizing the resolution behavior via the webpack.config.resolve property. material-ui seems to rely on resolving subdirectory imports from the module entry directory.

2. To distribute an ES module library, there's no need for building before distribution. However, projects such as create-react-app may need a pre-transpiled version.

Alternately, you can write import {Button} from 'components-library'. Webpack will trace the dependencies back through each index without a fuss.

Solution 4

you have to install babel-plugin-module-resolver package

Specify the package relative path in your .babelrc file alias like this

{
  "plugins": [
    ["module-resolver", {
      "alias": {
        "components-library": "./node_module/components-library"
      }
    }]
  ]
}

then you can import subdir of npm package like this

import { Button, ButtonGroup } from 'components-library/Button';

View more solutions

Comments

[Kendall]

I can't take the time to verify this in the context of the original answer (since I no longer have the project); however, it does appear to match what I now know about Webpack aliases, etc.

[matty]

Does this answer address the user's question? You may want to bring your skills and experience to questions tagged with angular.

[Hussein Akar]

Yes, If you follow my answer you could create a project with the same structure as martial-ui project. What they did is a workspace containing multiple packages this is called monorepo project structure. second part of the question where you could import you packages as import { componentName} from '@company/workspaceName' this is done in tsconfig.json and gave him the axcample from material-ui as follow: "paths": { "@material-ui/core": ["./packages/material-ui/src"], "@material-ui/core/*": ["./packages/material-ui/src/*"], .... } this is called creating fake path.

[Toivo Säwén]

Good answer. I found more information here: medium.com/swlh/npm-new-package-json-exports-field-1a7d1f489‌​ccf

[Toivo Säwén]

Typescript users: github.com/microsoft/TypeScript/issues/33079