请解释一下 event.emit('some_event'); console.log('some_event 事件触发'); 这一类代码都是什么意思

Question

var EventEmitter = require('events').EventEmitter; 

var event = new EventEmitter(); 

event.on('some_event', function() { 

    console.log('some_event 事件触发'); 

}); 

setTimeout(function() { 

    event.emit('some_event'); 

}, 1000);