您可以通过按索引访问jsonData.seats数组来实现这一点，最后一项的索引等于jsonData.seats.length-1
简单地说：

var countryId = jsonData.seats[jsonData.seats.length-1].countryid

试试这个：

var jsonObject = {
"expirationDate":"April 21, 2017",
"remainingDays":325,
"seats":[{"activeStatus":"S","pid":"TE70","firstName":"TE70","countryid":840},
        {"activeStatus":"Y","pid":"TE80","firstName":"TE80","countryid":845}]
 }

var lastElement = jsonObject.seats[jsonObject.seats.length-1].countryid

注：@ www.example.com 代码
使用DOT在
example.at(-1)

var jsonObject = {
        "expirationDate":"April 21, 2017",
        "remainingDays":325,
        "seats":[{"activeStatus":"S","pid":"TE70","firstName":"TE70","countryid":840},
                {"activeStatus":"Y","pid":"TE80","firstName":"TE80","countryid":845}]
                 }

var lastElement = jsonObject.seats.at(-1).countryid

你可以反转数组，然后得到第一个元素：el.reverse()[0]
例如：

var jsonObject = {
  "expirationDate": "April 21, 2017",
  "remainingDays": 325,
  "seats": [
    {"activeStatus":"S","pid":"TE70","firstName":"TE70","countryid":840},
    {"activeStatus":"Y","pid":"TE80","firstName":"TE80","countryid":845},
  ]
}

console.log( jsonObject.seats.reverse()[0].countryid ); //845

对于任何希望在JSONPath语法中实现这一点的人，可以使用$.seats[-1:]实现。如果你想做一些事情，比如获取嵌套在最后一个元素中的countryid属性，它应该是$.seats[-1:][countryid]。
这对于在API客户端中测试端点时链接请求很方便。