Answer 1

all(list) {
        return new Promise((resolve, reject) => {
            let resValues = [];
            let counts = 0;
            for (let [i, p] of list) {
                resolve(p).then(res => {
                    counts++;
                    resValues[i] = res;
                    if (counts === list.length) {
                        resolve(resValues)
                    }
                }, err => {
                    reject(err)
                })
            }
        })
    }

这么写的话是只要又一个promise失败, 整个.all 就失败了. 对业务是不是没那么友好