[How to make a Node Module run on Command Line and Required] #JavaScript

add.js

#!/usr/local/bin/node
#!/usr/bin/env node

const add = ( first, second ) => {
  return parseInt( first ) + parseInt( second );
}

/**
allows the javascript to be executed like this
 [14:08:27]/tmp $ ./add.js 1 2
 3
 [14:08:27]/tmp $ 

 or
 const add = require('./add');
 console.log( add(1,2) );
 **/

if ( require && require.main === module ) {
  console.log( add( process.argv[2], process.argv[3] ) );
} else {
  module.exports = add;
}

boomboom.js

/**
 * Example of how to test and behave differently if the command is
 * `required` vs called from cli via node as a script.
 *
 * eg: as a script
 *  node ./boomboom.js foo
 *  Hello foo
 *
 * eg: as a required function
 *  const boomboom = require('boomboom.js');
 *  boomboom('Something')
 */

const doSomething = ( message ) => {
  console.log('Hello', message);
}

if ( require.main === module  ){
  // running as a script
  doSomething( process.argv[2] );
}else {
  // this is being `required`
  module.exports = doSomething;
}