JS: numbers

index.js

var x = 3e2; // 300
var y = 3e-2; // 0.03

// only NaN dosen't equal to itself
function isNaN (number) {
  return number !== number;
}

// string -> number

// 1. isNaN - return false if string is not a NaN => it is a number
isNaN('123'); // false
isNaN(null); // false too :(

// 2. better isNumber
function isNumber (string) {
  // parseFloat - check "true/false/null/"
  // isInfinite - check "Infinite/-Infinite/NaN"
  
  return !isNaN(parseFloat(string)) && isInfinite(string);
}

// round numbers

Math.round(3.1) // 3
Math.ceil(3.1) // 4
Math.floor(3.1) // 3

// bitwise round
// all bitwise operators remove fractional part of number,
// so any operation that will not change the number, round it.
~~3.1 // 3
0.1 + 3 ^ 0 // 3