JSFiddle - React, Tailwind, and code Playground

JavaScript

var arr = [1, 7, 2, 3, 2, 1, 4, 5, 5, 1];

    function aclean (obj) {


        for ( var glav = 0; glav < obj.length; glav++) {

            for (var niz = 1; niz < obj.length; niz++) {
                if (obj[niz] == obj[glav]) obj[niz] = undefined;
            }
        }
        }
        
aclean(arr);
alert ( arr ); // 1,7,2,3,4,5