JSFiddle - React, Tailwind, and code Playground

JavaScript

function сomparison(a1, a2)
{
  var a=[], diff=[];
  for(var i=0;i<a1.length;i++)
    a[a1[i]]=a1[i];
  for(var i=0;i<a2.length;i++)
    if(a[a2[i]]) delete a[a2[i]];
    else a[a2[i]]=a1[i];
  for(var k in a)
    diff.push(a[k]);
  return diff
}
var visibleObjects = [124,125];
var allObjects = [124,125,126];
var wat = сomparison(allObjects,visibleObjects);
console.log(typeof wat[0]);