No Dupes in Array

function noDupes (arr) {
    var dict = {};
    var output = [];
    for (var i = 0; i < arr.length; i++) {
        if (!dict[arr[i]]) {
            dict[arr[i]] = 1;
        } else {
            dict[arr[i]]++;
        }
    }
    for (var key in dict) {
        if (dict[key] === 1) {
            output.push(key);
        }
    }
    return output;
}

console.log(noDupes([1,3,3,2,4]));