From MDN:

"Functions are one of the fundamental building blocks in JavaScript. A function in JavaScript is similar to a procedure—a set of statements that performs a task or calculates a value, but for a procedure to qualify as a function, it should take some input and return an output where there is some obvious relationship between the input and the output. To use a function, you must define it somewhere in the scope from which you wish to call it."

​

- Defining functions or function declaration or function statement

  - function keyword

  - parameters within parenthesis

  - statement within {}

  - Example 

    function double(number){

      return number * 2;

    }

  - The function double takes one parameter (number) and has one   statement that returns the provided number multiplied by 2.

- Calling functions

  - Example double(10);

  - Funcion declarations do not execute the function.  It needs to be called

- Parameters vs Arguments.  

  - Parameters are placeholders in functions or 'variables'

  - Arguments are the actual passed information

- In JavaScript you can pass functions to functions, meaning that a function can be an Argument.

*/

​

function setup() {

  createCanvas(400, 400);

  textSize(40);

}

​

function draw() {

  fill(255);

  text(double(4), width/2, height/2);

  if(logIt() % 20 === 0){

    background(220);

    text(logIt(), 200, 100);

  }

}

​

function double(num){

  return num * 2;

}

​

function logIt(){

  return floor(frameRate());

}