In this lab, you'll be building a small calculator function. Don't worry, your calculator will only need to add up numbers or subtract numbers. But, it will be doing it all from the command line!

1. Fork and clone this repository.

2. Navigate to the cloned repository's directory on your command line. Then, run the following command:

   npm install
   

   This will install the libraries needed to run the tests.

3. Open up the repository in VSCode. Follow the instructions below to complete the Lab.

Complete the calculator() function in the index.js file. This function will have no parameters -- instead, make use of process.argv to take in arguments from the command line. Use the tests, the JSDoc syntax, and the examples below to learn more about how the function should work.

To run the tests, you can run the following command from the command line. You will need to be in the root directory of your repository.

npm test

This will run the test output once.

If you want to manually test out your file, you can do so by running the following command.

node run.js

Add any arguments you want to test after the filename. For example:

node run.js plus 10 9 8

The output will be printed to your terminal.

If you'd like, you can have the tests run constantly. This means that each time you save your file, your tests will re-run. To do so, you can run the following:

npm run watch

Follow the on-screen prompts to exit out of the constant runner.

In order to simulate the command line, you'll see the following lines in the tests:

const command = "plus";
const numbers = ["5", "10"];
process.argv.push(command, ...numbers);

This is similar to running the following on the command line.

node index.js plus 5 10

The following are examples of what should happen when running the code from the command line.

Command line

node index.js plus 1 2 3 4 5

Result

15;

Command line

node index.js minus 10 5 1

Result

4;

Command line

node index.js divide 10 2

Result

"Invalid operation: divide";

Command line

node index.js minus

Result

"No numbers provided...";

Command line

node index.js

Result

"No operation provided...";

• Remember that the first and second elements of process.argv are always the path to the node program and the filepath.
• Remember that each argument from the command line will be read in as a string. You will need some way to convert the inputs from strings to numbers.
• Because you don't know how many numbers will be passed in, you may need to iterate over the numbers.