// Transform JSON array of stats into object
// concat values into single strings for each key
// ----------------------------------------------
function transform(json) {
    // iterate over each item in the JSON array
    // replace null values with empty strings
    // concat new value onto old value
    return json.results.reduce(function(acc, data) {
        return acc.then(prev => {
            return {
                one: (prev) 
                    ? `${prev.one},${data.one}` 
                    : data.one,
                two: (prev) 
                    ? `${prev.two},${data.two}`
                    : data.two,
                three: (prev) 
                    ? `${prev.three},${data.three}`
                    : data.three,
            };
        });
    }, Promise.resolve());
}

// Params for request, shouldn't need to modify this
// -------------------------------------------------
const options = {
    headers: {
        "Authorization": "Basic [base64 encoded hash]", // Add basic auth hash here
        "Content-Type": "application/json; charset=utf-8",
    },
}

// Configure endpoint to call
// --------------------------
const url = 'http://example.com';
const params = [
    'key=value',
];

// Magic happens here, make request to endpoint
// 1: resolve body of response
// 2: pass body to transform function
// 4: return error if encountered
fetch(`${url}?${params.join('&')}`, options)
    .then(res => res.json()) // [1]
    .then(transform) // [2]
    .catch(err => { throw new Error(err); }); // [4]