SOURCE

function createPipeFetch(limit, dataArr) {
    let _tmpFetchArr = [];
    function createFetch(data) {
        return new Promise((resolve, reject) => {
            setTimeout(() => {
                resolve(data);
            }, 3000)
        }).then(res => {
            console.log('data', data);
            dataArr.length > 0 &&  _tmpFetchArr.push(createFetch(dataArr.shift()));
        })
    }
    if (limit < dataArr.length) { // 如果最大并发数大于数组长度
        while(limit > 0) {
            _tmpFetchArr.push(createFetch(dataArr.shift()));
            --limit;
        }
    } else {
        [].concat(dataArr).forEach((item) => {
            _tmpFetchArr.push(createFetch(item));
            dataArr = [];
        })
    }
    return Promise.all(_tmpFetchArr);
}


createPipeFetch(2, [1,2,3,4,5,6,7])