map for object

map_for_object.js

Object.defineProperty(Object.prototype, 'map', {
    value: function(f, ctx) {
        ctx = ctx || this;
        var self = this, result = {};
        Object.keys(self).forEach(function(k) {
            result[k] = f.call(ctx, self[k], k, self); 
        });
        return result;
    }
});

looking for other way do not effect to Object.prototype