Why package.json in each component folder?

Why does each component get its own package.json, like this?

[jzelenkov]

it’s a convenience thing. It allows you to write a require statement for a directory instead of specific file.

without package.json:

import Layout from 'src/components/Layout/Layout.js'
// var Layout = require('src/components/Layout/Layout.js');

with package.json containing main keyword:

import Layout from 'src/components/Layout'
// var Layout = require('src/components/Layout');

Alternatively, one could rename Layout.js to index.js. Then require-statement resolution would work without package.json as well.

[koistya]

One of the use cases where package.json can be very helpful, is when you need to create an isomorphic component, having different implementations for Node.js and Browser environments:

{
  "name": "MyComponent",
  "version": "0.0.0",
  "private": true,
  "main": "./MyComponent.browser.js",
  "node": "./MyComponent.node.js"
}