In this lesson, you'll learn about functions in JavaScript, which are essential for organizing and reusing code efficiently.

Introduction

In this section, we're going to talk about functions. I'm really excited to show you how functions work! 😊 Functions are one of the most interesting and important parts of any programming language.

So what are functions, and why should we use them? A JavaScript function is a block of code designed to perform a particular task. Remember that: a block of code designed to perform a particular task. We often need to perform similar tasks many times in our application.

Functions are the main building blocks of a program. They allow the code to be called many times without repetition.

You've already seen a function in JavaScript. Not only have you seen it, but you've also used it multiple times by now. It was the function called . has the task of printing values to the console. After finishing this section, you'll be able to create your own functions as well! 😊

Now, let's dive right in!

When talking about functions, you're often going to hear two terms: and . So let's explain each one of these.

Function: A function is a special value with one purpose: it represents some code in your program. Functions are handy if you don’t want to write the same code many times. Calling a function like tells the computer to run the code inside it and then go back to where it was in the program. There are many ways to define a function in JavaScript, with slight differences in what they do.

Defining Functions

A consists of:

• the function keyword
• followed by the function name
• a list of parameters enclosed in parentheses
• and a block of code enclosed in {}

I'm first going to show you an example of a simple function called :

function square(number) {
  return number * number;
}

Let's break it down:

Let's break it down:

• : The reserved JavaScript keyword for creating a function.
• : The name of the function; you can name it however you'd like.
• : Inside the parentheses , we have parameters. These are values we'll send to our function when calling it. The function takes one parameter, called . You can name parameters however you'd like.

The function body, enclosed in curly braces {}, contains the code to be executed. In this example, it returns the parameter multiplied by itself.

The statement is crucial; it specifies the value that will be returned by the function. To retrieve values from functions, we need to call them.

Calling Functions

a function does not it. Defining it simply names the function and specifies what to do when the function is called.

the function actually performs the specified actions with the indicated parameters. For example, if you define the function , you could call it as follows:

square(5);

Here, we have the function name followed by parentheses. Inside the parentheses, we put .

Arguments are the values we want to pass to our parameters.

For example, if we send the of , the parameter becomes . The function then multiplies it by itself and returns the result.

As you can see, we get . Exactly as expected.

To use the from the function, we can store it in a :

const result = square(5);

This stores the return value of the function (called with an argument of ) in the variable. Now we can log it to the console:

console.log(result);

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