Simple timer on JS

timer.js

"use strict";
var Timer = function () {
    var _time = 0;
    var _interval = {};
    return {

        /**
         * Starts timer
         */
        start: function () {
            _interval = setInterval(function () {
                _time += 1;
            }, 1000);
        },

        /**
         * Set timer value (seconds)
         * @param {Number} value
         * @returns {boolean} False if data is not number
         */
        setValue: function (value) {
            if (value === Number(value)) {
                _time = value;
                return true
            }
            return false;
        },

        /**
         * Returns current timer value in seconds
         * @returns {number}
         */
        getValue: function () {
            return _time;
        },

        /**
         * Returns current timer value in hh:mm:ss
         * @returns {string}
         */
        getFormattedValue: function () {
            var sec_num = parseInt(_time, 10); // don't forget the second param
            var hours = Math.floor(sec_num / 3600);
            var minutes = Math.floor((sec_num - (hours * 3600)) / 60);
            var seconds = sec_num - (hours * 3600) - (minutes * 60);

            if (hours < 10) {
                hours = "0" + hours;
            }
            if (minutes < 10) {
                minutes = "0" + minutes;
            }
            if (seconds < 10) {
                seconds = "0" + seconds;
            }
            return hours + ':' + minutes + ':' + seconds;
        },

        /**
         * Stops timer
         */
        stop: function () {
            clearInterval(_interval);
            _time = 0;
        }
    }
};