Flatten Integer Array (Javascript)

// check if value is an integer
function isInt(value){
    return Number(value) === value && value % 1 === 0;
}

// function to flatten an array
function flatten(data, isInteger) {
    var result = [];

    // initialize data if input is undefined/empty
    data = data || [];

    // loop through the input array to process each element
    for (var i = 0; i < data.length; i++) {
        // check to see if the current item is an array itself
        if (Array.isArray(data[i])) {
            // if the item is an array then recursively call this function again and join the item to the result array
            result = result.concat(flatten(data[i], isInteger));
        } else {
            // once we find an item that isn't an array, push it to the result array.
            if (isInteger) {
                // if isInteger is true we will need to check whether the item is an integer before adding it to the result array
                if (isInt(data[i])) {
                    result.push(data[i]);
                }
            } else {
                result.push(data[i]);
            }
        }
    }

    // return the flatten array
    return result;
}


/* usage sample */

// input array
var inputArray = [[1,2,[3, [4]]],5, 'a', ['z', 6], 7, 8];
// flatten array
var outputArray = flatten(inputArray);
// flatten array with integer only
var integerArray = flatten(inputArray, true);