Undefined, Null, NaN, InfinityUnd, Nu, NaN, Inf studies// source https://jsbin.com/jimiku

jsbin.jimiku.js

// -----Undefined, Null, NaN, Infinity, -Infinity----- //

/* Undefined and null are both special values that signify the absence of meaningful
data. Undefined is considered its own data type, but null is considered an object by Javascript, 
which can be misleading. Null, more specifically, should represent the nonexistence of 
something. */

"use strict";

console.log(typeof undefined);

/* NaN stands for "not a number," and represents instances of calculations that do
not result in a precise or meaningful answer: */

console.log(1 * "what are you doing?"); // this is nonsensical

/* Using the typeof method on NaN will return "number", though it is not. */

/* Two other values that are grouped into the "number" type are the keywords Infinity and 
(-Infinity)--the former representing infinity into the positive integers and the latter 
into the negative integers. It is best not to trust infinity-based calculations, as they
will often lead to NaN. */

console.log(typeof -Infinity);