Learn
Functions
Return

When a function is called, the computer will run through the function’s code and evaluate the result of calling the function. By default that resulting value is `undefined`.

``````function rectangleArea(width, height) {
let area = width * height;
}
console.log(rectangleArea(5, 7)) // Prints undefined``````

In the code example, we defined our function to calculate the `area` of a `width` and `height` parameter. Then `rectangleArea()` is invoked with the arguments `5` and `7`. But when we went to print the results we got `undefined`. Did we write our function wrong? No! In fact, the function worked fine, and the computer did calculate the area as `35`, but we didn’t capture it. So how can we do that? With the keyword `return`! To pass back information from the function call, we use a return statement. To create a return statement, we use the `return` keyword followed by the value that we wish to return. Like we saw above, if the value is omitted, `undefined` is returned instead.

When a `return` statement is used in a function body, the execution of the function is stopped and the code that follows it will not be executed. Look at the example below:

``````function rectangleArea(width, height) {
if (width < 0 || height < 0) {
return 'You need positive integers to calculate area!';
}
return width * height;
}``````

If an argument for `width` or `height` is less than `0`, then `rectangleArea()` will return `'You need positive integers to calculate area!'`. The second return statement `width * height` will not run.

The `return` keyword is powerful because it allows functions to produce an output. We can then save the output to a variable for later use.

### Instructions

1.

Imagine if we needed to order monitors for everyone in an office and this office is conveniently arranged in a grid shape. We could use a function to help us calculate the number of monitors needed!

Declare a function `monitorCount()` that has two parameters. The first parameter is `rows` and the second parameter is `columns`.

2.

Let’s compute the number of monitors by multiplying `rows` and `columns` and then returning the value.

In the function body of the function you just wrote, use the `return` keyword to return `rows * columns`.

3.

Now that the function is defined, we can compute the number of monitors needed. Let’s say that the office has 5 rows and 4 columns.

Declare a variable named `numOfMonitors` using the `const` keyword and assign `numOfMonitors` the value of invoking `monitorCount()` with the arguments `5` and `4`.

4.

To check that the function worked properly, log `numOfMonitors` to the console.