将一个数组转化为需要的格式，来自react官网的商品列表示例

//原来的格式
const PRODUCTS = [
    { category: 'Sporting Goods', price: '$49.99', stocked: true, name: 'Football' },
    { category: 'Sporting Goods', price: '$9.99', stocked: true, name: 'Baseball' },
    { category: 'Sporting Goods', price: '$29.99', stocked: false, name: 'Basketball' },
    { category: 'Electronics', price: '$99.99', stocked: true, name: 'iPod Touch' },
    { category: 'Electronics', price: '$399.99', stocked: false, name: 'iPhone 5' },
    { category: 'Electronics', price: '$199.99', stocked: true, name: 'Nexus 7' }
];
//需要的格式  （就是把公共的标题提取出来了）
const res=[{ category: 'Sporting Goods' },
{
    product:
    {
        category: 'Sporting Goods',
        price: '$49.99',
        stocked: true,
        name: 'Football'
    }
},
{
    product:
    {
        category: 'Sporting Goods',
        price: '$9.99',
        stocked: true,
        name: 'Baseball'
    }
},
{
    product:
    {
        category: 'Sporting Goods',
        price: '$29.99',
        stocked: false,
        name: 'Basketball'
    }
},
{ category: 'Electronics' },
{
    product:
    {
        category: 'Electronics',
        price: '$99.99',
        stocked: true,
        name: 'iPod Touch'
    }
},
{
    product:
    {
        category: 'Electronics',
        price: '$399.99',
        stocked: false,
        name: 'iPhone 5'
    }
},
{
    product:
    {
        category: 'Electronics',
        price: '$199.99',
        stocked: true,
        name: 'Nexus 7'
    }
}]

let rows = [];
//记录最后一个分类的值，初始值为null
let lastCategory = null;
PRODUCTS.forEach(item => {
    if (item.category !== lastCategory) {
        rows.push({ category: item.category })
    }
    rows.push({ product: item })
    lastCategory = item.category;
})
console.log(rows)