Instructor: Let's first start by creating a directory called npx-test. We'll immediately change directories to our new folder. In order to start using Node modules, let's first create a package.json with npm init. You could provide the --yes flag or -y for short to automatically generate a package.json without it having to ask you questions.
It'll just use the default values. NPM will then print out the contents of the package.json for us to see. Sure enough, it looks legit. Now, let's install ESLint with npm install, or npm i for short, and save it as a dev dependency with --save-dev or -D for short.
If we cat our package.json, you'll see that there is now a dev dependency of ESLint. If we wanted to confirm that the package was actually installed, we could run the command npm -ls eslint. Yes, we have indeed installed ESLint locally.
For example, eslint --init. No, that does not work. It doesn't know about my locally installed version. It's looking for something that's globally installed. You could get around this by manually poking into your local Node modules bin folder in order to run ESLint.
That will work, but it's somewhat cumbersome, and not obvious at first. Another approach could be to leverage Unix command substitution, which takes the output from the npm bin command, and replaces the command itself.
Then proceed to invoke the locally installed ESLint. Likewise, this works, but it still could be better, which is where NPX comes into play. As long as you have NPM version 5.2 or above, then you're good to use NPX.
One of the many things it can do is allow you to invoke locally installed Node modules from the terminal. Here, we can npx eslint --init, and it'll work just fine. No more messy commands in the terminal.
Here, I'll pick a few options to get ESLint set up for us. Let's go with the standard style guide. Yes, we'll install the dependencies. Now, we have an ESLint RC file. At this point, you could start playing around with different commands from the terminal, leveraging the locally installed version of ESLint.
Here, for example, we see a couple of errors that it detected. If you feel good about this command, and want to promote it as an NPM script, then you could hop into the package.json file, and in the script sections, add a new script. In our case, we'll call it Lint. Its value, we'll type the same command that we had before.
Now, once we save our package.json, we could confirm that it does exist as a script. Sure enough, it does. Now, we could run the script from the terminal with npm run lint, and it works. You may have noticed there was a lot of extra noise on the terminal.
If that happens, and you'd like something a bit cleaner, you could try the command again, but this time, append the -s flag to run at the silent log level, which outputs much less results.