Failed to store an array within array nodejs

Question

I am working on a chat application. I have chat history in chats table. Now I want to see the latest message of each chat by using the sender email. So, I am getting the chat id by using distinct query as shown below

var userChat = [];

Chat.distinct("chatId", {"senderEmail" : req.params.Email}, function(err, result){
  if( result){
    console.log(result);

    for(var i = 0; i < result.length; i++){
      Chat.find({ chatId: result[i] }).sort('-_id').limit(1).exec(function(error, result) 
        {
        if(result){
          console.log(" IN FOR LOOP ");
          userChat.push(result);
        }
      });
    }  

    console.log("USER CHAT ARRAY :  ", userChat);

  }

});

After running the distinct query I got 4 chat ids [ '114143', '130997', '457884', '479310' ]

Now the problem is that whenever I call push then it is not pushing result array from find query into the userChat array. Also I have noticed that the console of USER CHAT ARRAY is called BEFORE for loop console. Following is the screenshot of the console

theBittor · Accepted Answer · 2020-03-24 18:37:55Z

1

Each Chat.find() operation is asynchronous, so your for loop creates and finished the iteration. By the time you hit console.log("USER CHAT ARRAY : ", userChat); none of this operations has finished yet.

Thats by you see USER CHAT ARRAY: [] and then IN FOR LOOP on the console.

You need to await each of this Chat.find() operations like so:

Chat.distinct("chatId", {"senderEmail" : req.params.Email}, async function(err, result){
  if( result){
    console.log(result);

    for(var i = 0; i < result.length; i++){
      try {
        var chat = await Chat.find({ chatId: result[i] }).sort('-_id').limit(1).exec();
        if(chat){
          console.log(" IN FOR LOOP ");
          userChat.push(chat);
        }
      } catch (e) {
        //Handle errors here
      }
    }  
    console.log("USER CHAT ARRAY :  ", userChat);
  }
});

The changes:

Mark Chat.distinct callback function with async
In for loop, await each Chat.find() query
Use try/catch to handle errors

edited Mar 24, 2020 at 18:37

answered Mar 24, 2020 at 18:02

theBittor

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2 Comments

user321 Over a year ago

Thank you for explaining. I tried it and I got a result in USER CHAT ARRAY but for chat id which is on index 0. It did not return the find result for chat ids that are on index 1 to 3.

theBittor Over a year ago

sorry I made a mistake, I use the result variable inside the for loop and has the same name as the variable from outside. I will change it to chat

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