Webpack: difference about entry between production and development environment - reactjs

Question

I'm reading tutorial about Webpack on this: Github Webpack tutorial In this, there is a section about config webpack for production and development.
Here is development configuration:
// webpack.config.dev.js
module.exports = {
devtool: 'cheap-eval-source-map',
entry: [
'webpack-dev-server/client?http://localhost:8080',
'webpack/hot/dev-server',
'./src/index'
],
Here is production configuration:
// webpack.config.prod.js
module.exports = {
devtool: 'source-map',
entry: ['./src/index'],
output: {
path: path.join(__dirname, 'dist'),
filename: 'bundle.js'
},
I understand the difference in option of devtool. The thing I don't understand about entry. Why in production, entry is only about src/index but in development configuration, entry also includes webpack-dev-server
'webpack-dev-server/client?http://localhost:8080',
'webpack/hot/dev-server',
'./src/index'

Answer 1

The lines 'webpack-dev-server/client?http://localhost:8080' and 'webpack/hot/dev-server' are configuring/defining which port to attach an active websocket to, in this case localhost:8080, and the content base which in this case is folder/path /client. In a production environment you would never run webpack-dev-server as your bundled client assets (bundle.js or similar) would be served by a server (IIS, Node, etc), that is why there are no webpack related items in entry of the production configuration.
The Webpack plugin in question webpack-dev-server is not required to run Webpack and compile your JS sources, it simply is a tool that can be used during the development process to watch for changes and reload changes.
Technically the entry array property in development could simply be the './src/index', but then it wouldn't enable the webpack-dev-server and/or it's hot module reloading. If you wanted to run webpack-dev-server without these configuration items then you'd then need to add command line arguments when starting webpack to specify the port and/or content base.
Hopefully that helps!

Answer 2

Here is the 2 things you should know before understanding:
As your linked in Webpack the confusing part, there are 3 types of entry: String Array and Object. As above code, that is array type. Meaning of entry array is: Webpack will merged all those javascript files in array together. This is often unnecessary because Webpack is intelligent enough to know which javascript files need to merge while processing. You often need to do this to enhance some features from different javascript files that you don't include somewhere else in your code.
This is "little tricky" part. You see webpack/hot/dev-serverand webpack-dev-server/client?http://localhost:8080 look like a web url rather than some javascript files, right? If you check your project directory, you see there are those files: your_app_directory/node_modules/webpack/hot/dev-server.js and your_app_directory/node_modules/webpack-dev-server/client.js. And that is the real meaning: you are importing two javascript files from two modules webpack-dev-server and webpack.
Back again to your webpack configuration:
entry: [
'webpack-dev-server/client?http://localhost:8080',
'webpack/hot/dev-server',
'./src/index'
],
That means we will merge three different javascript files together as point 2 I have figured out. As I explain in point 1, you will do this for enhancing some features. You include file webpack-dev-server/client.js for making a server for serving your code. You include file webpack/hot/dev-server.js for allowing your code autoloading. This is super useful when you in development mode without start/stop server each time you modify your code.