获取对象内对象数组的长度

Question

I would like to map the object and get the number/length of replies that can be found in replies in this case 2. I have fetched this data from the API and is unable to get the number of replies that can be found here.

let data = [ 
   { 
      "feedbackId":32,
      "sender":"12345"
      "comment":"Test Comment",
      "replies":[ 
         { 
            "feedbackLogId":32,
            "feedbackReplyLogId":1,
            "comments":"So this is 1",
            "createdBy":"Jack",
         },
         { 
            "feedbackLogId":32,
            "feedbackReplyLogId":2,
            "comments":"2nd one",
            "createdBy":"Min",
         }
      ],
   }
]

This is what I've done. I am only able to get 1 as the length.

let repliesToRender = data.map((item) => {item.replies})
let numReplies = repliesToRender.length

Answer 1

You have 2 issue in your code,

let repliesToRender = data.map((item) => {item.replies})

should be

let repliesToRender = data.map((item) => item.replies)

And map return you array so your repliesToRender will be an array of array so you need

let numReplies = repliesToRender[0].length

Or just

let numReplies = data.replies.length

---

 let data = [ { "feedbackId":32, "sender":"12345", "comment":"Test Comment", "replies":[ { "feedbackLogId":32, "feedbackReplyLogId":1, "comments":"So this is 1", "createdBy":"Jack", }, { "feedbackLogId":32, "feedbackReplyLogId":2, "comments":"2nd one", "createdBy":"Min", } ], } ] let repliesToRender = data.map((item) => item.replies) let numReplies = repliesToRender[0].length console.log(numReplies)

Answer 2

You can calculate reply per feedback using Array.prototype.map

for calculting total number of replies you can use Array.prototype.reduce

 let data = [{"feedbackId":32,"sender":"12345","comment":"Test Comment","replies":[{"feedbackLogId":32,"feedbackReplyLogId":1,"comments":"So this is 1","createdBy":"Jack"},{"feedbackLogId":32,"feedbackReplyLogId":2,"comments":"2nd one","createdBy":"Min"}]},{"feedbackId":32,"sender":"12345","comment":"Test Comment","replies":[{"feedbackLogId":32,"feedbackReplyLogId":1,"comments":"So this is 1","createdBy":"Jack"},{"feedbackLogId":32,"feedbackReplyLogId":2,"comments":"2nd one","createdBy":"Min"}]}] let repliesCount = data.map(({replies}) => replies.length); console.log('per replies',repliesCount); let totalCount = data.reduce((a,c) => a + c.replies.length, 0); console.log('total replies ',totalCount)

Answer 3

Another approach. This will run faster in case of large data-sets, as it's not using loops.

let data = [ 
   { 
      "feedbackId":32,
      "sender":"12345",
      "comment":"Test Comment",
      "replies":[ 
         { 
            "feedbackLogId":32,
            "feedbackReplyLogId":1,
            "comments":"So this is 1",
            "createdBy":"Jack",
         },
         { 
            "feedbackLogId":32,
            "feedbackReplyLogId":2,
            "comments":"2nd one",
            "createdBy":"Min",
         }
      ],
   }
]

let {replies} = data[0];
console.log(replies.length);

Answer 4

If replies count is needed for each of the objects, then below will return array of replies count for respective objects in order,

let eachObjectsRepliesCount = data.map(({replies}) => replies.length);

If replies count is needed for all the objects combined, then below will return the total replies count,

let repliesToRender = data.map((item) => item.replies)
let totalRepliesCount = repliesToRender[0].length