compose在Koa和Reduce中的几种实现

测试代码

const app = {
    middleWares: [],
    use(middleWarwe) {
        this.middleWares.push(middleWarwe)
    }
}
app.use((next) => {
    console.log(1);
    next();
    console.log(2);
});
app.use((next) => {
    console.log(3);
    next();
    console.log(4);
});

app.use((next) => {
    console.log(5);
    next();
    console.log(6);
});
app.compose()

koa 同步实现

app.compose = function () {
    const middleWares = this.middleWares
    function dispatch(index) {
      if (index === middleWares.length) return;
      const middleWare = middleWares[index]
      return middleWare(() => dispatch(index + 1))
    }
    dispatch(0)
}

koa 异步实现

app.compose = function () {
  const middleWares = this.middleWares
  function dispatch(index) {
    if (index === middleWares.length) return Promise.resolve();
    const middleWare = middleWares[index]
    return Promise.resolve(middleWare(() => dispatch(index + 1)))
  }
  dispatch(0)
}

reduce 同步

app.compose = function(){
  const middleWares = this.middleWares
  return middleWares.reduceRight((a,b)=>()=>b(a),()=>{})()
}

reduce 异步

app.compose = function(){
  const middleWares = this.middleWares
  return Promise.resolve(middleWares.reduceRight((a,b)=>()=>Promise.resolve(b(a)),()=>Promise.resolve())())
}

新reduce 同步

app.compose = function() {
  const middleWares = this.middleWares
  return middleWares.reduce((a, b) => arg => a(() => b(arg)))(() => {});
};

新reduce 异步

app.compose = function() {
  const middleWares = this.middleWares
  return Promise.resolve(middleWares.reduce((a, b) => arg => Promise.resolve(a(() => b(arg))))(() => Promise.resolve()));
};

async

app.compose = function(){
  const middleWares = this.middleWares
    return (async ()=>{
      let next = ()=>Promise.resolve()
      function createNext(middleWare,oldNext){
          return async ()=>{
              return await middleWarwe(oldNext)
          }
      }
      for(let i=middleWarwes.length-1;i>=0;i--){
          next = createNext(middleWarwes[i],next)
      }
  })()
}