[reactjs] What exactly is the 'react-scripts start' command?

As Sagiv b.g. pointed out, the npm start command is a shortcut for npm run start. I just wanted to add a real-life example to clarify it a bit more.

The setup below comes from the create-react-app github repo. The package.json defines a bunch of scripts which define the actual flow.

"scripts": {
  "start": "npm-run-all -p watch-css start-js",
  "build": "npm run build-css && react-scripts build",
  "watch-css": "npm run build-css && node-sass-chokidar --include-path ./src --include-path ./node_modules src/ -o src/ --watch --recursive",
  "build-css": "node-sass-chokidar --include-path ./src --include-path ./node_modules src/ -o src/",
  "start-js": "react-scripts start"
},

For clarity, I added a diagram.

The blue boxes are references to scripts, all of which you could executed directly with an npm run <script-name> command. But as you can see, actually there are only 2 practical flows:

• npm run start
• npm run build

The grey boxes are commands which can be executed from the command line.

So, for instance, if you run npm start (or npm run start) that actually translate to the npm-run-all -p watch-css start-js command, which is executed from the commandline.

In my case, I have this special npm-run-all command, which is a popular plugin that searches for scripts that start with "build:", and executes all of those. I actually don't have any that match that pattern. But it can also be used to run multiple commands in parallel, which it does here, using the -p <command1> <command2> switch. So, here it executes 2 scripts, i.e. watch-css and start-js. (Those last mentioned scripts are watchers which monitor file changes, and will only finish when killed.)

• The watch-css makes sure that the *.scss files are translated to *.cssfiles, and looks for future updates.

• The start-js points to the react-scripts start which hosts the website in a development mode.

In conclusion, the npm start command is configurable. If you want to know what it does, then you have to check the package.json file. (and you may want to make a little diagram when things get complicated).