v-model原理，用于监听window变量

window.power2 = {isShow:''};
Object.defineProperty(window.power2, 'isShow', {
get: function() {

return this._isShow;

},
set: function (val) {

this._isShow = val;
   console.log('?????', val, window.power2.isShow);

}
});
window.power2.isShow=false;