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);