Coercion in JavaScript

coercion.js

function isNeg0 (n) {
  return n===0 && (1/n)===-Infinity
}
if (!Number.isNaN) Number.isNaN = num => num !== num

// best way to do it in es6+
Object.is(0, -0)// false
Object.is(NaN, NaN)// true

var a = [1,5,3,4,8]
if (~a.indexOf(4)) console.log('Found 4 in a')
// ~N -> -(N+1)

var now = Date.now()// do not use +new Date()

var a = '42424'
var aNumber = Number(a)
var aString = String(aNumber)
var aBoolean = Boolean(aString)
// avoid calling new on String, Number, Boolean, Array, Object all times

// NEVER use == false or == true
'0' == false// true -- UH OH!
false == 0// true -- UH OH!
false == ''// true -- UH OH!
false == []// true -- UH OH!
'' == 0// true -- UH OH!
'' == []// true -- UH OH!
0 == []// true -- UH OH!