SOURCE

function unique(arr) {
    if (!Array.isArray(arr)) {
        console.log('type error!')
        return
    }
    var array = [];
    var obj = {};
    for (var i =0;i<arr.length;i++) {
        if(!obj[arr[i]]) {
            array.push(arr[i])
            obj[arr[i]] = 1
        } else {
            obj[arr[i]]++
        }
    }
    return array;
}
var arr = [2,2,8,8,9,0,null,null]
console.log(unique(arr))