How to send a message only to recipients from the list?

Question

JavaScript

After authorization, I enter socket.id into an array. How to send a message only to them?

socket.emit('block_item', {itemId: data.id});

Answer 1

Because the script is included in the head and the DOM has not yet been formed at the time the element is searched.

Answer 2

Because you need to store the DOM element you received earlier in a variable

var myElement = document.getElementById('message').innerHTML = 'Hello';

Answer 3

You don't need to put users in an array.
socket.io supports rooms (Room) or other channels.
You should simply add an authorized user to a specific room: and then send messages to the selected room(s):
More transmission options here