Step 7: Functions

We've been writing code that performs different actions, but sometimes you want to group code together to achieve a particular end. This is where functions come in.

A function is a block of code designed to perform a particular task. A function is executed when it is "invoked".

The syntax of a function looks like this:

function functionName (parameters) {  
  // code to be executed
}

You can call a function whatever you want, just like a variable. You can also give a function different values every time you run it which are called "parameters".

To make the function run, we invoke it like so:

functionName();

Try it out

Let's write a function that adds two numbers together. We'll call it add. We want to add together two different numbers every time, so let's define two parameters to represent this, x and y.

function add (x, y) {  
  // code to be executed
}

​add(2, 3);

Notice I've invoked the function underneath, with the parameters 2 and 3. Inside the function, try to console.log()both x and y and see what happens. Try logging them outside the function too. They will be undefined, because we can only access these parameters from inside the function.

function add (x, y) {  
  console.log(x);  
  console.log(y);
}

​add(2, 3);

Now, we want to add these two numbers together, but it isn't enough just to write x + y, since we haven't told the function to actually return anything. It's time for a return statement. This is usually how you end a function. The return statement specifies the value to output to the console.

function add (x, y) {  
  return x + y;
}

​add(2, 3);

Run this code, and hopefully you get the right answer!

Mini challenge

Write a function called multiply that multiplies two numbers together. It should take two numbers as parameters and return the answer.