null zero empty undefined

by Laurel Bruggeman

JavaScript

var a = 0;
var c = "";
var d = null;

if(typeof a === undefined) console.log('typeof a === undefined')
if(typeof b === undefined) console.log('typeof b === undefined')
if(typeof c === undefined) console.log('typeof c === undefined')
if(typeof d === undefined) console.log('typeof d === undefined')

if(typeof a == undefined) console.log('typeof a == undefined')
if(typeof b == undefined) console.log('typeof b == undefined')
if(typeof c == undefined) console.log('typeof c == undefined')
if(typeof d == undefined) console.log('typeof d == undefined')

if(typeof a === "undefined") console.log('typeof a === "undefined"')
if(typeof b === "undefined") console.log('typeof b === "undefined"')
if(typeof c === "undefined") console.log('typeof c === "undefined"')
if(typeof d === "undefined") console.log('typeof d === "undefined"')


if(!a) console.log('!a')
//if(!b) console.log('!b')
if(!c) console.log('!c')
if(!d) console.log('!d')

if(a) console.log('a')
//if(b) console.log('b')
if(c) console.log('c')
if(d) console.log('d')

if(a == null) console.log('a == null')
//if(b == null) console.log('b == null')
if(c == null) console.log('c == null')
if(d == null) console.log('d == null')

if(a != null) console.log('a != null')
//if(b != null) console.log('b != null')
if(c != null) console.log('c != null')
if(d != null) console.log('d != null')

if(a !== null) console.log('a !== null')
//if(b !== null) console.log('b !== null')
if(c !== null) console.log('c !== null')
if(d !== null) console.log('d !== null')

if(a === null) console.log('a === null')
//if(b === null) console.log('b === null')
if(c === null) console.log('c === null')
if(d === null) console.log('d === null')