JSFiddle - React, Tailwind, and code Playground

JavaScript

function findUnique(arr) {
    var result = new Set();
    // iterate through array
    for(var i=0; i<arr.length; i++) {
        var v = arr[i];
        if(result.has(v)) {
            result.delete(v);
        } else {
            result.add(v);
        }
    }
    // set to array O(n)
    var a = [], x = 0;
    result.forEach(function(v) { a[x++] = v; });
    return a;
}
alert(findUnique([1,2,3,0,1,2,3,5,4,4]));