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];

findCommon();

function findCommon()
{
    var common=[];
    for(i=0; i<a.length; i++)
    {
       if(b.indexOf(i) != -1 && c.indexOf(i) != -1 && d.indexOf(i) != -1) 
       {
          common.push(i);
       }
    }
   console.log(common);
}