JSFiddle - React, Tailwind, and code Playground

JavaScript

var cont_elem = [1, 2, 3, 4];
var no_cont_elem = [];
var comp_cont_elem = [1, null, undefined, 666 ];

function count(arr){
	var res = 0;
  
	for(var i = 0; i< arr.length; i++){
  	if ((arr[i] !== null) && (arr[i] !== undefined))
			res++;
	}
  
  return res;
}

alert("cont_elem " + count(cont_elem));
alert("no_cont_elem " + count(no_cont_elem));
alert("comp_cont_elem " + count(comp_cont_elem));