Socket.io array access

Question

I am making a simple app using socket.io and node.js and I have started to think about access to array from different events. So when somebody is joining to room I am pushing him to an array of all clients. Then I am looking for a specific client in an array to change some of his attributes. Finally when client disconnects I am removing him from array. Is there a chance that after function finds index of a specific client that client disconnects and the wrong client attribute will be changed? Here is piece of code

let array=[];

io.on('connection', function (client) {
  client.on('join',function(data){
    array.push(client);
  });
  client.on('message',function(data){
    let index= findOtherClientIndexInArray();
    if(index>-1){
        //If client leaves the array is altered so the index is not pointing at correct client
        array[index].attribute++;
    }
  });
  client.on('leave',function(data){
    array.splice(array.indexOf(client),1)
  });
});

What do you mean by "wrong client attribute will be changed"? Are you asking if a wrong client could be removed? Node.js being single-threaded should take care of what you're worried about either way, I belive. — hmiedema9
– hmiedema9, Commented Aug 29, 2018 at 14:36

Patrick Roberts · Accepted Answer · 2018-08-29 14:45:32Z

1

No, there is no risk of index no longer referring to the intended client in the array within a block of synchronous code, since Node.js is a single-threaded environment.

However, if I could make a suggestion for improving your maintainability a little, you could use a Set instead of an array:

let set = new Set();

io.on('connection', function (client) {
  client.on('join', function (data) {
    set.add(client);
  });

  client.on('message', function (data) {
    // return client directly instead of a key or index
    // return undefined or null if none is found
    let other = findOtherClientInSet();

    if (other) {
      other.attribute++;
    }
  });

  client.on('leave', function (data) {
    set.delete(client);
  });
});

answered Aug 29, 2018 at 14:45

Patrick Roberts

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1 Comment

user3102664 Over a year ago

Thank you for your answer and for suggesting using sets

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