Lab 4 i think: minus minus section

index.js

@@ -1,10 +1,39 @@
 /**
  * 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.
+ * 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() {}
+function calculator() {
+  let operator = process.argv[2]; //let operator = "operationName"
+  let sum = 0;
+
+
+  if (!operator) {//is there an operator?
+    return "No operation provided..."; //truthyness determined
+  } else if (operator !== "plus" && operator !== "minus") { //no math allowed
+    return "Invalid operation: " + operator;
+  }
+
+  const numbers = process.argv.slice(3); //look at every element after  [2]
+  //let numArray = [];
+   if (numbers.length === 0) { //are there less than 2 elements
+      //console.log("first", numbers.length)
+    return "No numbers provided...";
+  }
+
+  for( let num of numbers) { //iterate through [3] onwards
+   if (operator === "plus") {
+      sum += Number(num); //accumulate everything including && after [3]
+      }
+      else if (operator === "minus") {
+        return sum = numbers.reduce((previousVal, currentVal) => Number(previousVal) - Number(currentVal)) //accummulate the difference of numbers
+      }
+      } 
+  return sum;
+}
+
+calculator();
 
 // Don't change anything below this line.
 module.exports = calculator;