JSFiddle - React, Tailwind, and code Playground

JavaScript

function foo(bar) {
    return typeof bar === "undefined";
}  
var baz = null;
for(var i=0; i<10000; ++i) console.log("1", foo(baz))

for(var i=0; i<10000; ++i) console.log("2", typeof baz === "undefined")

function foo() {
  return typeof null === "undefined";
}

function bonc() {
    return typeof baz === "undefined";
}  
for(var i=0; i<10000; ++i) console.log("3", bonc())

for(var i=0; i<10000; ++i) console.log("4", (function(){
	return typeof baz === "undefined";
})());