JSFiddle - React, Tailwind, and code Playground

JavaScript

Array.prototype.foo = 10;
var  a = [1,2,3,4,5];

// exapple for inherited properties
function xyz()
{
  var ownProp = 'my prop';
}
xyz.prototype.inheritedProp = 'inherited prop';

var instOfxyz = new xyz;


// travers throug inherited properties also
function inStructOld(val,structure)
    {

      for(a in structure)
         {
           if(structure[a] == val)
             {
               return true;
             }
         }
       return false;
    }


// travers throug own properties 
function inStructNew(val,structure)
    {
      
      for(a in structure)
         {
            
           if(structure[a] == val && structure.hasOwnProperty(a))
             {
               return true;
             }
         }
       return false;
    }

alert(inStructNew(10,a));

alert(inStructNew('inherited prop',instOfxyz ));

alert(inStructOld('inherited prop',instOfxyz ));