

    var _hasDontEnumBug,
        _dontEnums;

    function checkDontEnum(){
        _dontEnums = [
                'toString',
                'toLocaleString',
                'valueOf',
                'hasOwnProperty',
                'isPrototypeOf',
                'propertyIsEnumerable',
                'constructor'
            ];

        _hasDontEnumBug = true;

        for (var key in {'toString': null}) {
            _hasDontEnumBug = false;
        }
    }

    /**
     * Similar to Array/forEach but works over object properties and fixes Don't
     * Enum bug on IE.
     * based on: http://whattheheadsaid.com/2010/10/a-safer-object-keys-compatibility-implementation
     */
    function forIn(obj, fn, thisObj){
        var key, i = 0;
        // no need to check if argument is a real object that way we can use
        // it for arrays, functions, date, etc.

        //post-pone check till needed
        if (_hasDontEnumBug == null) checkDontEnum();

        for (key in obj) {
            if (exec(fn, obj, key, thisObj) === false) {
                break;
            }
        }

        if (_hasDontEnumBug) {
            while (key = _dontEnums[i++]) {
                // since we aren't using hasOwn check we need to make sure the
                // property was overwritten
                if (obj[key] !== Object.prototype[key]) {
                    if (exec(fn, obj, key, thisObj) === false) {
                        break;
                    }
                }
            }
        }
    }

    function exec(fn, obj, key, thisObj){
        return fn.call(thisObj, obj[key], key, obj);
    }

    module.exports = forIn;


