JavaScript Awesome console Outputs

test.js

1. Both are same!
var obj = new Object(); //Empty Object
var obj = new Object; //same result

2. var obj = new Object(id: 1, name: "test");
Output > it will give error

3. 
var obj1 = {id: 1, name: "test"};
var obj2 = new Object(obj1); //obj1 and obj2 points to the same one
obj2.id = 2;
console.log(obj1.id); // 2

4. 
var arr1 = new Array(10);
arr1[0] = undefined but arr1.length = 10

5. var arr = Array.from("123"); 
   output > arr will be [1,2,3]


0/0 > NaN
1/0 > Infinity
-1/0 > -Infinity
-0/0 > NaN
"" /0 > NaN

typeof NaN > number
typeof Infinity > number
typeof -Infinity > number
typeof undefined > 'undefined'
typeof undefined == undefined  > false
typeof undefined == 'undefined' > true
typeof null > 'object'
typeof -null > number
typeof "" > string
typeof -"" > number
typeof -"mohit" > number  : -"mohit" gives result NaN 

console.log("-Mohit") > -Mohit
console.log(-"Mohit") >  NaN
But -"Mohit" == NaN  false 

NaN == NaN > false  because NaN never equal to anyone

undefined == undefined > true

isNaN(0/0)  > true 
isNaN(NaN) > true
isNaN("mohit") > true
isNaN("") > false
isNaN("12") > false
isNaN(-"12") > false
isNaN(-"mohit") > true

"" == [] > true
0 == [] > true
0 === [] > false
[] == [] > false because it is same as new Array() == new Array()
{} == {} > false because it is same as new Object() == new Object() 
[] == false > true
[] == true > false 

(null < 0) >> false
null > 0 >> false
null < Infinity >> true
null < -Infinity >> false

console.log(!0) > true because it is same as !false 
console.log(!'0') > false because it is same as !true

var obj  = {a :1, b: 2, c: 3};
what will output for below?
for (let item in a) {console.log(item)} // a b c
for (let item of obj) {console.log(item)} // Uncaught TypeError: obj is not iterable


x = 5;
console.log(x);
var x;
output > 5

var x = 10;
console.log(x);
var x;
console.log(x);
output > 
   10
   10


var x;
console.log(x);
var x = 12;
console.log(x);
output >
   undefined
   12

var x = 1;
console.log(x, y);
var y = 6;
output > 1 undefined

[] + []
output > ""

{} + {}
output > "[object object][object object]"

[] + "hello".split('')
output > "h,e,l,l,o" // because it first convert to string before concatenate.

console.log('undefined' + undefined);
undefined = null;
console.log(undefined);
output > 
   undefinedundefined
   undefined


console.log(x);
x = 45; // it will not be hoisted because it is not declearted by var.
output >  ReferenceError: x is not defined




JAVASCRIPT SET VS ARRAY
https://medium.com/front-end-weekly/es6-set-vs-array-what-and-when-efc055655e1a