[j0hnik]

Alexandroppolus,

var arr = [1,1,2,5,9,9,7,7];

function unq(arr) {
	var obj = {};
	for(var i = 0;  i < arr.length; i++){
		var num = arr[i];
		obj[num] ? delete obj[num] : obj[num] = 1;
	}
	return Object.keys(obj).map(n=>+n);
}

console.log(unq(arr));