> **timers**: this phase executes callbacks scheduled by setTimeout() and setInterval().
**pending callbacks**: executes I/O callbacks deferred to the next loop
iteration.
**idle, prepare**: only used internally.
**poll**: retrieve new I/O events; execute I/O related callbacks (almost
all with the exception of close callbacks, the ones scheduled by timers,
and setImmediate()); node will block here when appropriate.
**check**: setImmediate() callbacks are invoked here.
**close callbacks**: some close callbacks, e.g. socket.on('close', ...).