let list = [...this.list]; //為什麼這裡要解構賦值？ Oberver，Watcher和Dep

https://segmentfault.com/a/1190000009054946

filteredAndOrderedList () {

let list = [...this.list]; //為什麼這裡要解構賦值？

// 按品牌过滤

if (this.filterBrand !== '') {

list = list.filter(item => item.brand === this.filterBrand);

}

// 按颜色过滤

if (this.filterColor !== '') {

list = list.filter(item => item.color === this.filterColor);

}

// 排序

if (this.order !== '') {

if (this.order === 'sales') {

list = list.sort((a, b) => b.sales - a.sales);

} else if (this.order === 'cost-desc') {

list = list.sort((a, b) => b.cost - a.cost);

} else if (this.order === 'cost-asc') {

list = list.sort((a, b) => a.cost - b.cost);

}

}

return list;

}