promise基于reduce实现队列消息

function dosomething(num) {

    return new Promise((resolve, reject) => {

        setTimeout(() => {

            console.log(num);

            if(num > 4) reject(num);

            else resolve(num);

        }, num * 1000);

    });

}

function queue(arr, thing) {

    return arr.reduce((promise, params) => 

                new Promise((resolve, reject) => {

                    promise.then(results => {

                        thing.call(null, params).then(r => {

                            resolve([...results, r]);

                        }).catch(e => {

                            reject(e);

                        });

                    })

                }),

                Promise.resolve([]));

}

queue([4, 1, 3, 2], dosomething).then(res => {
    console.log('succes', res);
}).catch(err => {
    console.log('error', err);
});

// 输出
// 4
// 1
// 3
// 2
// succes [4, 1, 3, 2]