发布订阅事件+异步函数说明

1. 监听触发事件：

class EventEmeitter {
    constructor(){
        this._events = this._events || new Map();
        this._maxLength = this._maxLength || 10;
    }
}

EventEmeitter.prototype.$on = function(type,fn){
    const handle = this._events.get(type);
    if(handle){
        handle.push(fn);
    }else{
        this._events.set(type,[fn])
    }
}
EventEmeitter.prototype.$emit = function(type,...args){
    const handle = this._events.get(type);
    for(let i=0;i<handle.length;i++){
        handle[i].apply(this,args);
    }
}

const emitter = new EventEmeitter()
emitter.$on('arson', man => {
  console.log(`expel ${man}`);
});
emitter.$on('arson', man => {
  console.log(`save ${man}`);
});

emitter.$on('arson', man => {
  console.log(`kill ${man}`);
});
// 触发事件
emitter.$emit('arson', 'low-end');

2. 异步函数

async函数就是Generator函数的语法糖
async/await其实是基于Promise的
也就是 async/await是基于promise，用generator的语法糖实现的：

var promise = (prama)=>{
    return new Promise((resolve,reject)=>{
        setTimeout(()=>{
            resolve(prama);
        },2000)
    })
}
var genPromise = function *(){
    yield promise('入参')
}
var gen = genPromise();
gen.next().value.then((val)=>{
    console.log(val);
})
var asyncFun = async function(){
    var one = await promise('rucan2');
    return one;
}
asyncFun().then((val)=>{
    console.log(val);
})

async/await 就是

getConstant() {
   return 1
 }

 async getAsyncConstant() { 
  return 1
 }

 async getPromise() {
  return new Promise((resolved, rejected)=> {
    resolved(1)
  });
 }

 async test() {
  let a = 2
  let c = 1
  await getConstant();
  let d = 3
  await getPromise();
  let d = 4
  await getAsyncConstant();
  return 2
 }

使用了 promise进行了包裹

function getConstant() {
   return 1;
}

function getAsyncConstant() {
  return Promise.resolve().then(function () {
   return 1;
  });
}

function getPromise() {
  return Promise.resolve().then(function () {
   return new Promise((resolved, rejected) => {
    resolved(1);
   });
  });
}

  test() {
    return Promise.resolve().then(function () {
       let a = 2;
       let c = 1;
       return getConstant();
     }).then(function () {
       let d = 3;
       return getPromise();
     }).then(function () {
       let d = 4;
       return getAsyncConstant();
     }).then(function () {
       return 2;
     });
 }