javascript_functions.md

#JavaScript Functions

##Objectives

- Understand what a JavaScript function is
- Be able to recognize a function syntax
- Understand how to write a constructor function

###What is a JavaScript function?

In JavaScript, a function can be both a method AND a class.

###Using JS functions as a subroutine

A JavaScript function is essentially a block of code to do a particular task. Sometimes you will hear them being referred to as methods or subroutines. In the Object-Oriented Programming (OOP) paradigm, think of it like behaviors.

• To use JavaScript as a method, you will have to 1) define the method and 2) invoke it.

Demo

// Define our function with a parameter name

function sayHi(name){
	// write a message saying hi
	console.log('Hi, I am ' + name);
}

// Invoke our function with the argument 'Stanley'

sayHi('Stanley');

####Activity

---

Write a function that does a square root of any integer argument and test it on the numbers 4, 6, and 22

#####Part II

Write a check in the function that ensures only a number can be inserted. Return false if the parameter is not an integer

Solution:

function squareRoot(num){
  if(typeof num==='number' && (num%1)===0){
	return num * num;
  }else{
	return false;
  }
}

console.log(square(4));
console.log(square(6));
console.log(square(8));
console.log(square('hello world'));

#####Part III

Partner up with the person next to you and create a JS function that convert Fahrenheit to Celsius

function toCelsius(fahrenheit){
	return (fahrenheit - 32)/(1.8);
}

console.log(toCelsius(100));

###What the heck is a class?

A class is a simply template to create objects!

For instance, let's create a human class

// Define the class
function Human(name){
	
	this.name = name;
	this.sayHi = function(){
		console.log('Hi, my name is ' + this.name);
}

// Initialize the object utilizing the 'new' keyword
var Stanley = new Human('Stanley');
Stanley.sayHi();

###What the heck is this

The this keyword in javascript, in a constructor function context, refers to the the Object once its been initialized with the new keyword.

However, keep in mind, in a global context, this refers to the window object

####Activity

---

Now, make your person be able to calculate the square root of numbers

Then

Make your person be able to convert fahrenheit to celsius!

###Questions

• What are the two main purposes of using functions in JavaScript?
• What is this keyword refer to in the global context?
• What is the syntax for writing a basic subroutine?