Watcher in javascript.

watcher.js

var Watcher = function ()
{

    var _interval   = 1000;

    var _running    = false;

    var _callback   = function ()
    {
        // Just a callback
    };

    var _watcher    = this;

    var _runner     = function ()
    {
        if (true === _watcher.isRunning()) {
            _watcher.getCallback().call(null);
            window.setTimeout(_runner, _watcher.getInterval());
        }
    };

    this.getCallback = function ()
    {
        return _callback;
    };

    this.setCallback = function (callback)
    {
        if (typeof(callback) !== 'function') {
            throw 'Invalid callback.';
        }
        _callback = callback;
        return this;
    };

    this.getInterval = function ()
    {
        return _interval;
    };

    this.setInterval = function (interval)
    {
        if (isNaN(interval)) {
            throw 'Invalid number';
        }
        _interval = interval;
        return this;
    };
    
    this.isRunning = function ()
    {
        return _running;
    };

    this.start = function ()
    {
        _running = true;
        _runner();
        return this;
    };
    
    this.stop = function ()
    {
        _running = false;
        return this;
    };

};