JSFiddle - React, Tailwind, and code Playground

JavaScript

console.clear();

function a(b) {
	console.log(b);
	console.log(!b);
	console.log(typeof b);
	
	console.log(b != undefined);
	console.log(b !== undefined);
	
	console.log(b == null);
	console.log(b === null);
}

var arr = [1,2];
var b		= [arr][2];

a();
console.log("-----------------------------");
a(b);