Review

• Data Types (arrays, bools, etc)
• Control Flow (if/else/for/while)

What Is a Function

Functions

• Are encapsulated (self-contained)
• Have scope
• Can be invoked

Lets Write A Function

function helloWorld() {
  console.log( 'Hello World!' )
}

Invoking A Function

// define the function
function helloWorld() {
  console.log( 'Hello World!' )
}

helloWorld() // invoke the function
// => 'Hello World'

Function Parameters

Parameters allow functions to become more reusable 

// name is a parameter
function helloPerson( name ) {
  console.log( 'Hello ' + name + '!' )
}

helloPerson('Ramsay')
// => 'Hello Ramsay'

// Lets use some numbers because Math!

var startingNumber = 1

function doubleNumber( number ) {
     return number * 2
}


doubleNumber(startingNumber)
// => 2

doubleNumber(10)
// => 20

Returning Values From Functions

Returning Values From Functions

Side Effects vs Output

Side Effect

var num = 10

function multiplyNumber( multiple ) {
  num *= multiple;
}

multiplyNumber( 5 )
// => num = 50

multiplyNumber( 2 )
// => num = 100

Output

var num = 10

function multiplyNumber( multiple ) {
  num *= multiple;
}

multiplyNumber( 5 )
// => num = 50

multiplyNumber( 2 )
// => num = 100