Алексей Струков

function formatter(item) {
    return "0" + item.toString();
}

function validator(number) {
    if (typeof number !== "number") {
        throw new Error("invalid argument: Number expected");
    }
    return number;
}

function formatData(array, formatter, validator) {
    return array.map(item => formatter(validator(item)));
}

alert(formatData([1, 2, 3], formatter, validator));

/**
     * @param {Array} settings.arr
     * @param {Number} settings.valueToFind
     * @param {Function} settings.comparator
     *
     * @returns {Number|undefined}
     */
    function findClosest(settings) {

      var lo                 = -Infinity,
            hi                 = Infinity,
            arr                = settings.arr,
            valueToFind = settings.valueToFind,
            comparator  = settings.comparator,
            result;

        for (var i = 0; i < arr.length; i++) {

            if (arr[i] <= valueToFind && arr[i] >= lo) {
                lo = arr[i];
                continue;
            }

            if (arr[i] >= valueToFind && arr[i] <= hi) {
                hi = arr[i];
            }
        }

        result = comparator(lo, hi, valueToFind);

        return isFinite(result) ? result : undefined; // or false
    }

var comparator1 = function(lo, hi, valueToFind) {
        return lo; // or hi
};

var comparator2 = function(lo, hi, valueToFind) {
        var result = lo; // or hi

        switch (true) {
            case valueToFind - lo < hi - valueToFind:
                result = lo;
                break;
            case valueToFind - lo > hi - valueToFind:
                result = hi;
                break;
        }

        return result;
};
 
var settings = {
        arr: [1, 5, 10, 8, 5, 13],
        valueToFind: 7,
        comparator: comparator2
};