一个promise面试题

Question

有一个数组，里面都是promise的实例。代码实现如下要求：每次执行数组里的前n个实例，在这n个promise实例执行完后（即这n个promise的状态都是Fulfilled或Rejected）再开始下次n个实例执行，直到数组里的实例都被执行完

Answer 1

(function (){
    let data=[1,2,3,4,5,6,7,8,9];
    let n=4;
    function executePromiseGroup(dataList,groupSize){
        let _dataList_ = [...dataList];
        let finalResultData = [];
        return new Promise((resolve,reject)=>{
            let groupIndex = 0; 
            let _next_ = (groupIndex)=>{
                let _promise_all_data_ = _dataList_.splice(0,groupSize);
                if(_promise_all_data_.length===0){
                    resolve(finalResultData);
                    return;    
                }
                Promise.all(_promise_all_data_.map((data)=>{
                        return new Promise((resolve,reject)=>{
                            setTimeout(()=>{
                                 if(data === 4){
                                    resolve('模拟异步请求发生错误啦:'+data);
                                 }else{
                                    resolve('group_index:'+groupIndex+'>>'+data);
                                 }                           
                            },100);
                            //此处处理异步请求，在此处catch异步异常情况，然后resolve
                        });
                })).then((resultDataList)=>{
                    finalResultData = finalResultData.concat(resultDataList);
                    _next_(++groupIndex);
                });
            }

            _next_(groupIndex);
        });

    }
    executePromiseGroup(data,n).then((data)=>{
        console.log(data);
    })
}());