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JavaScript Declarations are Hoisted
Functions declarations are also hoisted
JavaScript Initializations are Not Hoisted


typeof undefined           // undefined
typeof null                // object
null === undefined         // false
null == undefined          // true

var cars = ["BMW", "Volvo", "Saab", "Ford", "Fiat", "Audi"];
cars.length   // gives size

cars.sort();  // only sorts alphabets not number array
cars.reverse();    

// to sort number array
var points = [40, 100, 1, 5, 25, 10];
points.sort(function(a, b){return a - b});

Array.isArray(cars);  // returns true
var temp = "";
Array.isArray(temp);  // returns false


// other method to check the type is using 
// 'constructor' property
<script>
var fruits = ["Banana", "Orange", "Apple", "Mango"];
document.getElementById("demo").innerHTML = isArray(fruits);

function isArray(myArray) {
    return myArray.constructor === Array;   // this will return true
}
</script>

// similarly
<script>
var myDate = new Date();
document.getElementById("demo").innerHTML = isDate(myDate);

function isDate(myDate) {
    return myDate.constructor === Date;   // this will return true
}
</script>


// reason 
new Date().constructor   // this returns --- function Date() { [native code] }

// converts anything to string 
String(x)         
x.toString()

// converts string to number
Number("3.14")    // returns 3.14
Number(" ")       // returns 0 
Number("")        // returns 0
Number("99 88")   // returns NaN
Number(false)     // returns 0
Number(true)      // returns 1

5 + null    // returns 5         because null is converted to 0
"5" + null  // returns "5null"   because null is converted to "null"
"5" + 2     // returns 52        because 2 is converted to "2"
"5" - 2     // returns 3         because "5" is converted to 5
"5" * "2"   // returns 10        because "5" and "2" are converted to 5 and 2

Boolean("0");   // retunrs true ******
Boolean(0);   // retunrs false ******

// function - written inside the object

<script>
var person = {
    firstName: "John",
    lastName : "Doe",
    id       : 5566,
    fullName : function() {
       return this.firstName + " " + this.lastName;
    }
};

// constructor

<script>
function person(firstName,lastName,age,eyeColor) {
    this.firstName = firstName;
    this.lastName = lastName;
    this.age = age;
    this.eyeColor = eyeColor;
    this.changeName = function (name) {
        this.lastName = name;
    }
}
var myMother = new person("Sally","Rally",48,"green");
myMother.changeName("Doe");
document.getElementById("demo").innerHTML =
"My mother's last name is " + myMother.lastName;
</script>


// javascript prototype is a constructor only

// valid
<script>
var x = function (a, b) {return a * b};
document.getElementById("demo").innerHTML = x(4, 3);
</script>

// valid
// Function constructor
<script>
var myFunction = new Function("a", "b", "return a * b");
document.getElementById("demo").innerHTML = myFunction(4, 3);
</script>