🚄Node On Rails: Bootstrapping the CLI tool

Last time we created an essential repo, and today, we will start to implement our first small CLI tool.

Installing dependencies

We will need to install the following dependencies.

yarn add colors commander

and the following dev dependencies

yarn add -D @types/node typescript  ts-node rimraf

The dev dependencies are our typical friends if we work with typescript. @types/node are the needed type definitions for typescript. typescript is, of course, typescript 😏. ts-node will it make easy to run typescript directly and at least we have rimraf which is a package that can delete folders.

Setting up the package.json

We now need to define some npm scripts to make it easier to run our project.

...
"scripts": {
        "dev": "ts-node src/index.ts",
        "build:clean": "rimraf lib",
        "build": "yarn run build:clean && tsc && chmod +x ./lib/index.js",
}
...

"dev": This will run our index.ts directly. We don't need to build our project and compile our typescript code to javascript
"build:clean": This will delete our build folder.
"build": Here, we are telling yarn first to clean the build and then to compile the typescript and build our project. The chmod +x ./lib/index.js is important. It will make our index.js executable so that we can run it as a binary.

We need to add one last thing to our package.json, and this is the bin key.

    "bin": {
        "nor": "./lib/index.js"
    },

Now we can run our build version the following way:

yarn run nor

And also if the user installs this package, he will be able to type

nor

Typescript config

{
  "compilerOptions": {
    "target": "ES2018",
    "module": "commonjs",
    "sourceMap": true,
    "outDir": "lib/",
    "strict": true,
    "types": [
      "node"
    ],
    "esModuleInterop": true,
    "forceConsistentCasingInFileNames": true,
    "removeComments": true
  },
  "include": [
    "src/**/*"
  ],
}

The upper JSON is a basic tsconfig.json file. One important key is outDir. outDir tells the Typescript compiler were to pit the build. "include" tells the Typescript compiler where to look for .ts files. It will look into all folders inside the src/ folder, including the src folder. If you want to know more about the tsconfig.json write it down below in the comments.

Our first command

Now that we have our package.json ready to go. We can now implement our first CLI command.

Create src/index.ts. You can do it like this.

mkdir src
touch src/index.ts

Now open the index.ts and add the following line:

#!/usr/bin/env node

the code above will tell the UNIX system you are running this bin on to use nodejs. It does a little bit more. If you want to read more about it, here is a Wikipedia link.

Importing commander and our first command

import program from 'commander'.

program
    .command('hello <name>')
    .description('Prints the given namen')
    .action((name: string) => {
        console.log(`hello ${name})
    })

program.parse(process.argh)

To make this one easier to understand. Save the file and type the following command into your terminal

yarn run dev hello devto

The command should print hello devto. Okay, now let us see how it works.

First, we import the commander package. Then we will create our hello command. command() is the part after the binary name or yarn run dev. Looking back at our example command, it would be hello devto. "hello " is now simple to understand. "hello" is the command, and is a parameter.

The description() is the text we will see when we see the help output.

And now the action() part. Here happens the actual work. The first argument is a callback, and the first argument of that callback is the first parameter from our command. In our case <name>. We are taking that string and just printing it out for now.

program.parse awaits some input. We want to give it the argh(arguments) from the terminal.

That's it! We have built our first command CLI tool.

Building and running our tool

We have already set up our build. We only need to run

yarn run build

If everything went fine, you should now have a lib/ folder.
You can run the script directly with

node lib/index.js

another way is to run

yarn run nor

If you want to see the help page, you can run

yarn run nor -h
//or
yarn run nor --help

Next steps

We will extend this package and start to implement the new command. With the new command, we want to create a new project.

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