Strange usage in node-mysql documantation

Question

while reading the node-mysql documantation i saw a usage as i pasted below

var query = connection.query('SELECT * FROM posts');
query
  .on('error', function(err) {
    // Handle error, an 'end' event will be emitted after this as well
  })
  .on('fields', function(fields) {
    // the field packets for the rows to follow
  })
  .on('result', function(row) {
    // Pausing the connnection is useful if your processing involves I/O
    connection.pause();

    processRow(row, function() {
      connection.resume();
    });
  })
  .on('end', function() {
    // all rows have been received
  });

i wonder how they use this events those can be used with the name whatever user names the query query in example when i create custom events i name them first for example var foo=new events.EventEmitter and after this in whole page i have to use it as foo.on("someEvent") but here they somehow bind the var created by user as event name in example code user names the mysql query as query and the event emitter has the same name somehow

and second question how is that possible to chain events as they use

.on("event").on("anotherEvent")

this question may sound strange but i really wonder how this works and it will change my code design completely

Answer 1

query is just your variable name for what is an instance of a Query in the node-mysql lib. You get access to all the functions that object exports.

on is inherited from EventEmitter in the node.js core. The key thing is that calling on returns "itself" i.e. this:

Returns emitter, so calls can be chained.

This allows you to chain calls to on