javascript - 从链中解决 promise

Question

场景是这样的，我收到一个 get 请求，它触发了一个返回 Promise (promise1) 的函数，Promise 返回函数本身有一个 promise 链。 现在我不想等到链结束后再将响应发送到前端，而是想在中间的某个地方解决。

现在问题的其余部分作为注释放在代码中，这样更有意义。

app.get('/data', (req, res)=>{

    promise1()
    .then(result=>{     
        res.status(200).send({msg:result});     
    })
    .catch(result=>{
        res.status(400).send({msg:"Error"});
    })
})

let promise1 = ()=>{
    return new Promise((resolve, reject)=>{
        promise2()
        .then(result=>{
            resolve(result);
        /*What I want here is, just after the promise2 is resolved I want 
        to send the result back to the get router, so I can give quick response
        and continue the slow processing in the backend which is promise3, but this
        does not work as expected, I do not get the result in the router until promise3 is 
        resolved. But I do not want that. So any suggestions on how to achieve that.
        */

            return promise3()           
        })
        .then(result=>{
            console.log("Done");            
        })
        .catch(err=>{                       
            console.log(err);           
        })      
    })
}

let promise2 = ()=>{
    return new Promise((resolve, reject)=>{ 
        resolve("Done");        
    })
}

let promise3 = ()=>{
    return new Promise((resolve, reject)=>{     
        //Slow Async process
        resolve("Done");        
    })
}

可以通过将 promise3 放入 setTimeout 来做到这一点，但我不确定 如果那是正确的方法。

请忽略任何语法错误，这只是为了给出问题的思路。

此外，我不确定这是否是正确的做法 - 如果我错了请纠正我。

Answer 1

糟糕，看来我作为 How to properly break out of a promise chain? 的副本过早关闭了.你真正想要的隐藏在源代码的注释中:

Just after the promise2 is resolved i want to send the result back to the get router so i can give give quick response and continue the slow processing in the backend which is promise3, but

return promise3()

does not work as expected, i do not get the result in the router until promise3 is resolved.

这更像是 Can I fire and forget a promise in nodejs (ES7)? - 是的你可以。您只需要return 要从函数发回的结果，以便 promise 链继续处理并立即发送。缓慢的后端处理将通过调用它来启动，但不会通过将它返回到链中来等待它:

function promise1() {
    return promise2().then(result => {

        // kick off the backend processing
        promise3().then(result => {
            console.log("Backend processing done");
        }, err => {
            console.error("Error in backend processing", err);
        });
        // ignore this promise (after having attached error handling)!

        return result; // this value is what is awaited for the next `then` callback
    }).then(result => {
        // do further response processing after having started the backend process
        // before resolving promise()
        return response;
    })
}