JSFiddle - React, Tailwind, and code Playground

JavaScript

var myArr = [1, 1, 2, 5, 5, 7, 8, 9, 9];
var map = new Object();

for(var i = 0; i < myArr.length; i++)
{
    if(map[myArr[i]] === undefined)
    {
        map[myArr[i]] = 1;
    }
    else
    {
        map[myArr[i]]++;
    }
}

var result = new Array();

for(var i = 0; i < myArr.length; i++)
{   
    if(map[myArr[i]] > 1)
    {
        //do nothing
    }
    else
    {
        result.push(myArr[i]);
    }

}

alert(result);