编写一个 People 类，使其的实例具有事件绑定、触发事件、解除绑定功能。

Question

/* * TODO * */People.prototype.sayHi = function () {    console.log('Hi, I am ' + this.name)}// 目标效果：var jerry = new People('Jerry')jerry.sayHi() // => 输出：'Hi, I am Jerry'jerry.on('greeting', say)jerry.on('greeting', say2)jerry.emit('greeting', 'Hi') // => 输出：'Hi, nice meeting you.' 和 'Hi, nice meeting you, too'jerry.off('greeting', say)jerry.emit('greeting', 'Hi') // => 只输出：'Hi, nice meeting you, too'function say (greeting) {  console.log(greeting + ', nice meeting you.')}function say2 (greeting) {  console.log(greeting + ', nice meeting you, too')