promise retry实现

retry(pf,{
    times: 3,
    //每次延迟
    delay: 1000,
    //每次延迟增量
    increment: 1000,
    shouldRetry: (err,opts) => {
        //判断是否应该继续
        return true;
    },
    onRetry: (data) => {
        //收集error和次数信息
    }
})
.then(data => console.log(data))
.catch(err => console.log(err));


//then链实现
function retry(promiseGen,opts){
    return promiseGen().catch(err => {
        if(opts.shouldRetry && !opts.shouldRetry(err,opts)) return Promise.reject(err);
        if(opts.times-- < 1) return Promise.reject(err);
        let starter = opts.delay ? delay(opts.delay) : Promise.resolve();

        return starter.then((res) => {
            if(opts.onRetry) opts.onRetry({err,times:opts.times});
            opts.delay += opts.increment || 0;

            return retry(promiseGen,opts);
        })
    })
}

//await实现，使用await可以直接在for循环中操作，非常清晰
async function retry(promiseGen,opts){
    let res,err;
    let errors = [];
    let starter = Promise.resolve();

    for(var i=0;i<=opts.times;i++){
        try{
            res = await starter.then(promiseGen);
        }
        catch(e){
            err = e;
        }

        if(!err) return Promise.resolve(res);

        errors[i] = err;
        err = null;

        if(opts.delay) {
            starter = delay(opts.delay);
            opts.delay += opts.increment || 0;
        }
    }
    return Promise.reject({errors,times:i})
}

function delay(time){
    return new Promise(resolve => setTimeout(resolve, time))
}