Java脚本承诺-如果语句返回最佳实践

Question

I'm writing a node.js function that returns a different promise depending on a condition, the cod:

if(condition){
    return promise.then(() => {
        return Promise.resolve(value)
    })
}else{
    return anotherPromise
}

Now the problem is that if the condition is true, I need to something after the promise is fulfilled, but in the other case I just return the promise, so the eslint tells me that it's a bad practice to nest promises. So this code won't work for me:

(() => {
    if(condition){
        return promise
    }
    }else{
        return anotherPromise
    }
}).then(() => {
    return Promise.resolve(value)
})

Because using this code the then callback will be executed in the two cases.

What is the best practice to handle this case?

Answer 1

If you use classic (ES6 / ES2015+) Promise syntax you have to chain promises (nothing bad with it!).

But you have also option to split the code into functions to gain readability and avoid nesting issues :

const firstCase = () => ... // returning a promise
const secondCase = () => ... // returning a promise

if (condition) {
  return firstCase()
} else {
  return secondCase()
}

But with ES7/ES2016+ you can use async/await syntax:

// in a "async" function
async function main() {
  if (condition) {
    await promise // if you need the promise result, you can assign it
    return value // the result of an async function is always a Promise.
  } else {
    return anotherPromise
  }
}

or mix both solutions.

Answer 2

A simple suggestion, (this should work) pass the condition in the resolve's argument and check it in the then block. The pseudo-code below will clarify it better:

(() => {
    if(condition){
        return new Promise((resolve,reject)=>{
            //Some tasks
            resolve(condition)

            //Some reject condition
            reject()
        })
    }
    else {
        return new Promise((resolve,reject)=>{
            //Some tasks
            resolve(condition)

            //Some reject condition
            reject()
        })
    }
}).then((condition) => {
     if(condition) {
         //Do something
     }
     else {
        //Do Nothing
     }
})

Answer 3

eslint tells me that it's a bad practice to nest promises.

Just tell it to shut *** up disable the linter on this statement. Promises have the ability to be nested precisely so that you can nest them when you need it, and this is one of those cases. Your code is fine.

Answer 4

Seems like you are over complicating it. The then method already returns a promise so you don't need to put a Promise.resolve inside it.

You can for simplicity do

return condition
  ? promise.then(() => value)
  : anotherPromise