index.js

/**
 * The function below has no parameters. Instead, access the arguments from the command line.
 * The first argument passed after the filename should be either "plus" or "minus", which represents the kind of calculation that will be done. Every argument afterwards should be a number.
 * Depending on the operation, either add up all of the numbers or subtract all of the numbers, from left to right.
 * @returns {number} The result of either adding all numbers or subtracting all numbers, depending on the arguments added to the command line.
 */
function calculator() {
let result = Number(process.argv[3]);
if (!process.argv[2]){
    return 'No operation provided...'}

if (!process.argv[3]) { 
   return 'No numbers provided...'}

if (process.argv[2] !== 'plus' && process.argv[2] !== 'minus'){
    return `Invalid operation: ${process.argv[2]}`}

if (process.argv[2] === 'plus'){
    for(let i = 4; i < process.argv.length; i++){
        result += Number(process.argv[i])}
}
if (process.argv[2] === 'minus'){
    for(let i = 4; i < process.argv.length; i++){
        result -= Number(process.argv[i])} 

}return result 
}

// Don't change anything below this line.
module.exports = calculator;