Node.js, Accept arguments from the command line

When invoking a Node.js application on the terminal you can pass any number of arguments and arguments can be standalone or have a key and a value.

For example, let consider the below command

node app.js jose

What happens in a nutshell node.js expose an argv property, which is an array that contains all the command line invocation arguments.

The first element is the full path of the node command, the second element is the full path of the file being executed and all the additional arguments are present from the third position going forward, to check this out see the snippet below.

process.argv.forEach((val, index) => {
   console.log(`${index}:${val}`);
});

You can get only the additional arguments by creating a new array that excludes the first 2 params:

const args = process.argv.slice(2);

This said consider the below snippet

const args = process.argv.slice(2);
console.log(args);

We can execute this program now

node app.js jose

Here is the result

jose

Now that we know how to accept arguments from the command line, let us built a simple calculator on top of this knowledge

const args = process.argv.slice(2);
let result = 0;

if(args.length === 0){
    console.log('Pass two numbers to add');
    process.exit(1);
}
if(args.length <= 1){
    console.log('We need two numbers to add them');
    process.exit(1);
} 

args.forEach((value) => {
    result += parseInt(value);
});

console.log(`The sum of ${args[0]} with ${args[1]} is ${result}.`);