JSFiddle - React, Tailwind, and code Playground

JavaScript

var array = [{qn : 0, points : "2"}, {qn : 1, points :"2"}, {qn : 2, points : "6"}, {qn : 2, points : "2"}, {qn : 3, points : "3"}]
var temp = [];
$.each(array, function (key, value) {
   if($.inArray(value.qn, temp) === -1) {
        temp.push(value.qn);
    }else{
       console.log(value.qn+" is a duplicate value");
    }
});