把数组对象中的值相加把那个放入最外层的对象里

var orders = that.data.orderList
//orders是需要操作的数组对象 需要把orderDetailList数组里的itemNum值相加放在该对象的最外层 orderTotal
var orderTotalArr = []
for (var i = 0; i < orders.length;i++){
var num = 0
for (var j = 0; j < orders[i].orderDetailList.length;j++){
num += orders[i].orderDetailList[j].itemNum
}
orders[i].orderTotal = num

}
that.setData({
orderList: orders,
})
orders就是我们最终想要的数组对象