Today we're going to be building the back end for a basic calculator. Don't worry, it's way easier than it sounds!

This is a test-driven app. You'll do all of your work in calculate-back-end.js, and within that file, you'll be making just one function, called calculate. Look at the tests in calculate.test.js for reference, as well as the test descriptions in your terminal.

• Note that the numbers are being passed in as strings, but the return value should be in numbers. What's more, some of the math may be funky if you try to do the math while they're still strings. Be sure to look into how to convert a string to a number in JavaScript!
• if/else chains and switch are good ways to check which operation you were passed. But whether you use those or another operation-checking method, you'll definitely want to branch your logic based on the contents of that string.
• Don't conflate the symbols and their mathematical operations. There's no good way to use the '+' string--instead you want to check the operation's string and, if it's '+', return a sum. Think of the '+' string as no different than the string 'plus'--you'll have to handle both, and while only one of them is a JavaScript operator, they're both strings you can check against expected values.