Use a function by its name somewhere in a program.

function doSomething(){}
doSomething();

If you've made a function in your program, it can work as a block in other parts of your program. To use your function you make a function call. This is like calling a friend for help. The function has code inside of it that will do something to help your other code. So, you call your function for help to get something done now. Like this:

let side = 0;
let volume = 0;
function cubeit() {
    volume = side * side * side;
}

side = 15;
cubeit();
side = 21;
cubeit();

In the example, the cubeit function is called twice to calculate the volume of some cubes with different sizes. The code in the function stays in one place. It doesn't have to get copied to the program everyplace you want to calculate a cube volume. This is really convenient! Your code is reusable.

define