vue 是怎么实现响应式的

            var vm = {};
            var data = {
                name: ‘zhangsan‘,
                age: 18
            }
            var key , value;
            for ( key in data) {
                (function(key) {
                    
                    Object.defineProperty(vm,key,{
                        get: function() {
                            console.log(‘get‘);
                            return data[key];
                        },
                        set: function(newValue){
                            console.log(‘set‘);
                            data[key] = newValue;
                        }
                    })
                    
                })(key)
            }