Outline for Monday, September 28th

• Review Wednesday's exercises
• Functions

Defining a function

var greeting = function() {
  console.log("Hello World");
};

greeting();

Defining a function with a parameter

var greeting = function(firstName) {
  // anything inside of here will execute when the function is called
  console.log("Good morning " + firstName);
};

var name = "Otis";
var name2 = "Bodhi";
greeting(name);
greeting(name2);

Defining a function with two parameters

var greeting = function (name, question) {
  // anything inside of here will execute when called
  console.log("Good morning", name, question);
  console.log("name:", name);
  console.log("question:", question);
};

greeting('Jenny', 'how was your weekend?');

var name = "Bernie";
var question = "how is the campaign?";
greeting(name, question);

Why use functions?

Functions are the bread and butter of JavaScript programming. The concept of wrapping a piece of program in a value has many uses. Functions are used to structure larger programs, to reduce repetition, to associate names with subprograms, and to isolate these subprograms from each other.

Let's greet some instructors

var instructor = "Caleb";
console.log("Hello " + instructor); // Hello Caleb

var instructor = "Jenny";
console.log("Hello " + instructor); // Hello Jenny

// let's greet some students too

var student = "Nathan";
console.log("Hello " + student);  // Hello Nathan

var student = "Rachel";
console.log("Hello " + student); // Hello Rachel

So what does this have to do with functions?

The questions we should be asking are:

1. Did we repeat ourselves in our code?
2. Can we make our program simpler?
3. Can we make our program easier to maintain?

var greeting = function(person) {
  // We can avoid re-writing the same code by placing the repeated code inside of a function
  console.log("Hello " + person);
};

// Now let's greet some instructors...
greeting("Caleb");
greeting("Jenny");

// ... and some cats.
greeting("Otis");
greeting("Bodhi");

###Functions make our code easier to maintain

var greeting = function(person) {
  // With just 1 change, we can adjust our program output
  console.log("Hola " + person);
};

// Now let's greet some people...
greeting("Bernie Sanders");
greeting("Donald Trump");

Returning values

The keyword return halts the execution of the function and returns the desired value for use in the rest of your code.

var sum = function(x,y) {
  return x + y;
}

var summedNumber = sum(3,4);
var yourNumber = 3;

var newNumber = yourNumber + summedNumber;

console.log(newNumber);

##Putting the 'fun' in function() You know the drill...open main.js and begin!!