const install = function (Vue) { 
    const Bus= new Vue({ 
        methods : { 
            emit (event, ... args) {
                this.$emit (event, ... args);
            },
            on (event, callback) { 
                this.$on (event, callback); 
            },
            off (event, callback) { 
                this . $off(event, callback); 
            }
        }
    })
    Vue.prototype.$bus = Bus; 
}
export default install