JSFiddle - React, Tailwind, and code Playground

JavaScript

var a = [11, 2, 3, 4],
    b = [2,  6, 3, 5],
    c = [4, 2, 20, 3],
    d = [34, 2, 21, 5],
    result = [],
    common = [];

function findCommon () {	
	for(var i = 0; i < arguments.length; i++){
		var garr = arguments[i];
		result = result.concat(arguments[i]);
	};
}
findCommon(a,b,c,d);

var sorted_arr = result.sort();

for(var i = 0; i< result.length-1; i++){

	if(result[i+1] == sorted_arr[i]){
		common.push(result[i]);
	}
};

alert(common);