Javascript - 尝试使用 Array.lenght 访问 foreach 循环中每个数组的最后一个元素

Question

I need to display preview of user text messages from an array. I achieve this easily if I hardcode the number in the loop. It works but it's not pretty. A prettier solution would be to display last text message received or sent. My attempt at doing this with Array.Length is failing miserably because not all users have the same number of text messages. If a user has 4 messages and another 2 messages, then it will cause an undefined error when looping over the users with less messages. How can this be done?

txt.details[0].message //works but not pretty

function

function getSMS(){
usersms.forEach(function (txt,counter) {
//
//
//get total number of msgs per user
var usertxtarray = txt.details;
var length = (usertxtarray).length;
console.log('msgs per user : ' + length);//prints 2, 2, 4

//display sms preview
var sms = (txt.details[length].message).substring(0,35) + '...';

//etc... 

});
}

Here's what (txt.details) looks like

[
  {
    "direction": "from",
    "user": {
      "id": "23",
      "avatar": "myavatar.jpg",
      "first_name": "Jane",
      "last_name": "Doe",
    },
    "message": "Lorem ipsum dolor sit amet, 😆😆 consectetur adipiscing elit",
    "smsid": "2220",
    "date": "202-12-29",
    "time": "12:00",
    "timezone": "Eastern Standard Time"
  },
  {
    "direction": "to",
    "user": {
      "id": "23",
      "avatar": "myavatar.jpg",
      "first_name": "Jane",
      "last_name": "Doe",
    },
    "message": "Lorem ipsum dolor 😍 😎sit amet, consectetur adipiscing elit",
    "smsid": "2220",
    "date": "2021-01-05",
    "time": "09:00",
    "timezone": "Eastern Standard Time"
  }
]

Answer 1

Arrays are zero-indexed.

So if your length = 4, then your last item is at index 3.

So...

var sms = txt.details[length - 1].message.substring(0, 35) + '...';

will give you the last message.