两个数组，重复的属性覆盖，不重复的添加

问题描述：

B2B后台：关于添加商品的问题，添加一些商品，如果添加的商品在原商品中存在，则覆盖其数量，不存在则添加

例：arr1 = [ {"externalCommodityCode" : "690123456001","commodityCode" : "200010825","saleAmount" : 20.0},

　　　　　　{"externalCommodityCode" : "690123456002","commodityCode" : "200010826","saleAmount" : 10.0,} ]

　　arr2 = [ {"externalCommodityCode" : "690123456002","commodityCode" : "200010826","saleAmount" : 20.0},

　　　　　　{"externalCommodityCode" : "690123456003","commodityCode" : "200010827","saleAmount" : 10.0} ]

最后得到 => arr1 = [ {"externalCommodityCode" : "690123456001","commodityCode" : "200010825","saleAmount" : 20.0},

　　　　　　　　{"externalCommodityCode" : "690123456002","commodityCode" : "200010826","saleAmount" : 20.0},

　　　　　　　　{"externalCommodityCode" : "690123456003","commodityCode" : "200010827","saleAmount" : 10.0,} ]

arr2.forEach(item => {
    let num = 0
    arr1.some(val => {
        num++
        if (val.externalCommodityCode === item.externalCommodityCode) {
            val.saleAmount = item.saleAmount
            return true
        } else if (num === arr1.length) {
            arr1.push(Object.assign({}, item))
        }
    })
})