标题：钩子函数 题目描述：请实现一个钩子函数，钩子函数可以理

import React, {component} from 'react'

export default class Listener extends React.Component {
    constructor(props) {
        super(props);
        this.state={
            count:1
        }
    }
    componentDidMount() {
        window.addEventListener('click',this.handle)
    }
    
    componentWillUpdate() {
        window.removeEventListener('click', this.handle)
    }
    
    handle = () => {
        if(this.state.count >1) {
            this.setState({
                count: count+1
            })
        }
    }
    
    render() {
        return (
            <div>
             <button onClick={this.handle}>submit</button>
            </div>
        )
    }
} 

class EventEmitter {
  constructor() {
    this._observerList = []
  }
  
  subscribe(observerFunc) {
    if (!observerFunc instanceof Function) throw new Error('param must be a function')
    return this._observerList.push(observerFunc) 
  } // end subscribe
  
  notify() {
    this._observerList.forEach(func => func())
  } // end notify
} // end EventEmitter

const _eventEmitterInstance = new EventEmitter()

_eventEmitterInstance.subscribe(()=>console.log('one'))

_eventEmitterInstance.subscribe(()=>console.log('two'))

_eventEmitterInstance.subscribe(()=>console.log('three'))

_eventEmitterInstance.notify()