Node.js - Socket.io

Last Updated: 2022-03-26

Duplicated Response

A common mistake when start using Socket.io is to put socket.emit() right next to socket.on(), which seems natural.

function foo() {
  socket.emit('req');
  socket.on('res', function (data) {
    console.log(data);
  });
}

However this will result in duplicated actions, since every time foo() is called, one res is registered. To fix this, move socket.on() out of the function, make sue it is only called once.

function foo() {
  socket.emit('req');
}

socket.on('res', function (data) {
  console.log(data);
});