JavaScript: Basic Variable & Function usage #JavaScript #Functions

JavaScript: Var & Function.js

var variableName; //undefined
var helloWorld = "Hello, World!";
var ten = 10;
var pi = 3.14;
var isBoolean = false;

var sum = 4 + 5,
    difference = 4 - 5,
    product = 4 * 5,
    quotion = 4 / 5;

//Function declaration syntax 
//hoisted, meaning you can place this function anywhere, and call this function anywhere
//JS Engine place it into the top of your code
function doSomething(){};

//Function as Object
//not hoisted. You can only call this function after the function is defined
var doSomething = function(){};

//this keyword, refers to global object, window (if executed in browser)
//or current execution context
alert( this.parseInt("10.2", 10) ); // 10
alert( this.parseFloat("3.14159") ); // 3.14159