README.md

Using Our Functions

We can make our functions a lot more complicated than just logging statements.

For example, if you were a coffee shop owner, you could create a function to calculate the total cost of a latte:

function latteTotal() {
  const price = 4.50;
  const salesTaxRate = .10;
  const totalAmount = price + (price * salesTaxRate);
  console.log("The total is $" + totalAmount);
}

But, what if you wanted to calculate the price of an Americano? Should you write another function called americanoTotal() that performs the same calculation with a different price? What about calculating the prices of scones or donuts? Writing all of these functions doesn’t sound like DRY code, does it?

Introducing Parameters

We can give the function different information to work with using parameters. Instead of doing the same thing with the same information each time, we have the function perform the same tasks on any data we give it.

Remember how we’ve been leaving the () after our function’s name empty? It’s time to throw some parameters in there. Here’s how we’d refactor the latteTotal() function to work for any product in our coffee shop:

function calculateTotal(price, salesTaxRate) {
   const totalAmount = price + (price * salesTaxRate);
   console.log("The total is $" + totalAmount);
}

A few things to note:

• There’s nothing special about the words price or salesTaxRate. We’re using descriptive names to remember what information we’re providing our function. It’s up to you to choose parameter names that make sense for what you’re trying to do.
• We can add multiple parameters separated by commas in the parentheses.

From Parameters to Arguments

When we invoke a function, we replace parameters with the data we want them to actually use. The data we provide when invoking a function is called an argument.

Here’s how we’d invoke a function with arguments:

function calculateTotal(price, salesTaxRate) {
   const totalAmount = price + (price * salesTaxRate);
   console.log("The total is $" + totalAmount);
}

calculateTotal(4.50, .10);

In this example, 4.50 corresponds to price and .10 corresponds to salesTaxRate. The order the arguments are written is important, because it tells JavaScript which parameters they represent.

Hello, You!

Now that we know about parameters, let’s make a friendly function that can greet anybody by their name.

• Define a function named sayHello.
• It should have one parameter for the name of the person we’re greeting.
• It should log the message Hello _____!, filling in the name in the blank.

Solution