JSFiddle - React, Tailwind, and code Playground

HTML

<pre><code id="output"></code></pre>

JavaScript

function removeDuplicates(arr) {
    var counts = {};
    for(var i=0; i<arr.length; i++) {
        var item = arr[i];
        counts[item] = (counts[item]||0)+1;
    }
    var arr = [];
    for(item in counts) {
        if(counts[item] === 1) {
            arr.push(item);
        }
    }
    return arr;
}

var myArr = [1, 1, 2, 5, 5, 7, 8, 9, 9];
var newArr = removeDuplicates(myArr);
document.getElementById("output").textContent = JSON.stringify(newArr);