function dispath(){
    console.log('異步3完成，異步2才能開始，異步2完成，異步1才能開始')
    //創(chuàng)建任務一
    let blockOperationOne = new BlockOperation((b)=>{
        console.log('異步1任務');
        //單一任務完成事件通知
        b.finished();
    });

    //添加新任務
    blockOperationOne.addExecutionBlock((b)=>{
        console.log('異步1新增任務');
        b.finished();
    });

    //創(chuàng)建任務二
    let blockOperationTwo = new BlockOperation((b)=>{
        console.log('異步2任務');
        b.finished();
    });

    blockOperationTwo.addExecutionBlock((b)=>{
        console.log('異步2新增任務2');
        b.finished();
    });

    blockOperationTwo.addExecutionBlock((b)=>{
        console.log('異步2新增任務需要等待4秒');
        setTimeout(() => {
            console.log('異步2新增任務3');
            b.finished();
        }, 4000);
    });

    //創(chuàng)建任務三
    let blockOperationThree = new BlockOperation((b)=>{
        console.log('異步3需要等待1秒');
        setTimeout(() => {
            console.log('異步3任務');
            b.finished();
        }, 1000);
    });

    //添加依賴
    blockOperationOne.addDependency(blockOperationTwo);
    blockOperationTwo.addDependency(blockOperationThree);

    //開始執(zhí)行
    blockOperationOne.start();
    blockOperationTwo.start();
    blockOperationThree.start();

    console.log('我是宏任務');
};

//任務通知對象
class Block{
    //完成回調(diào)
    doneCallBack = null
    constructor(doneCallBack){
        this.doneCallBack = doneCallBack
    }

    //單任務完成
    finished(){
        this.doneCallBack();
    }
}

//任務對象
class BlockOperation {
    //任務集合
    blocks = []
    //是否已開始
    isBeginStart = false
    //依賴任務對象
    dependencyOperation = null
    //被依賴影響的對象
    impactOperation = null
    //全部完成的事件判定
    allOperationIsDone = false
    //全部完成的事件回調(diào)
    allOperationDoneBlock = ()=>{
        //將依賴任務完成進行自身任務
        if(this.impactOperation){
            this.impactOperation.start()
        }
    };

    //代理
    proxy = null;
    //代理set方法
    handler = {
        set(target,property,value){
            target[property] = value
            if(property == 'allOperationIsDone' && value){
                //執(zhí)行閉包回調(diào)
                target.allOperationDoneBlock();
            }
            return true
         },
        get(target,property){
            return target[property]
        }
    }

    //初始化
    constructor(cb){
        this.blocks.push(cb)
        this.addObserver()
    }

    //添加觀察者
    addObserver(){
        this.proxy = new Proxy(this, this.handler)
    }

    //添加新任務
    addExecutionBlock(cb){
        this.blocks.push(cb)
    }
    
    //添加依賴
    addDependency(blockOperation){
        this.dependencyOperation = blockOperation
        blockOperation.impactOperation = this
    }

    //開始異步任務
    start(){
        const self = this
        self.isBeginStart = true
        //先判斷是否有依賴
        if(this.dependencyOperation && this.dependencyOperation.allOperationIsDone == false){
            //這里加一個定時器（目的是添加一個相對靠后的宏任務來檢查所有的任務是否都執(zhí)行了開啟，不是很嚴謹）
            setTimeout(()=>{
                if(self.dependencyOperation.isBeginStart == false){
                    throw Error('請檢查是否有依賴任務未開啟')
                }
            },0)
            //等待依賴的執(zhí)行完
            return
        }
        self.blocks.forEach((operationBlock) => {
            Promise.resolve(operationBlock).then((res)=>{
                if(res){
                    res(new Block(()=>{
                        //刪除任務
                        delete self.blocks[self.blocks.indexOf(res)]
                        //過濾null（防止delete執(zhí)行后數(shù)組中有null占位）
                        self.blocks = self.blocks.filter((item) => {
                            return item
                        })
                        //判斷是否全部完成
                        self.proxy.allOperationIsDone = (self.blocks.length == 0)
                    }))
                };
            })
        });
    }
}