NodeJS - 如何在继续执行流程之前等待多个异步调用完成？

Question

I have a function getAliasesByRoleDetailed(role) that takes care of fetching user data given a role (this function uses axios to fetch data).

The output of this function is something like this:

[     
    {
        alias: 'xxxx',
        Role: 'Admin',
        grantedBy: 'rnfnf',
        timestamp: '1591375676333'
    },
    {
        alias: 'vbjp',
        Role: 'Admin',
        'Granted By': 'hjkds',
        timestamp: '1588013678236'
    }
]

It is possible to do something like this:

const response = await getAliasesByRoleDetailed(role);

and then keep doing stuff with response once the data is available.

But what if I want to make multiple calls to this getAliasesByRoleDetailed(role) function and .push() the results into an array before moving on with the code execution?

1. I want to execute the getAliasesByRoleDetailed(role) for each element in an array like ['Admin','Trainer','Manager'] and push the results of each execution into a resultsArray .
2. After all calls have finished and the results are available in the resultsArray , I'd like to continue with my logic, using the resultsArray data.

So, ideally:

//Inside a function...

[getting data using getAliasesByRoleDetailed(role) ...]

resultsArray.forEach( (e) => {
    //Do something useful with all these element I now have!
}

I've tried a couple of solutions with async/await and .forEach() but keep getting stuck. Is there a simple solution for this?

Answer 1

If I understand your question correctly, you'd probably want to make use of Promise.all .

This will wait for all the inner promises (promises passed into the function) to resolve before resolving itself.

// inside an async function

const roles = ['Admin', 'Trainer', 'Manager'];

const results = await Promise.all(roles.map(role => {
  return getAliasesByRoleDetailed(role);
}));

// results should now have all the results available

You can then flatten the array using Array.flat

// inside the same function
const flattenResults = Array.flat(results);

Answer 2

Since you mentioned async/await, I assume that getAliasesByRoleDetailed returns a Promise . Therefore, you have to do something like

let resultsArray = await Promise.all(['Admin','Trainer','Manager'].map(getAliasesByRoleDetailed))

Answer 3

let result = await data.reduce(async (promise, value) => {
        await promise;

        let response = await getAliasesByRoleDetailed(value.Role);
        //do something with response
        return response;
      }, Promise.resolve());

Answer 4

You could consider to use Promise.all: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/all

In your situation, you can try this:

Promise.all(['Admin','Trainer','Manager'].map(getAliasesByRoleDetailed)).then(resultsArray => {
  // do your stuff
})

Answer 5

Use Promise.all or Promise.allSettled Promise.all will resolve only when all of the promises have resolved hence why I think you should probably use Promise.allSettled() as it waits for all promises to complete regardless if one of them is rejected

 roles=['Admin','Trainer','Manager'] var result=Promise.allSettled(roles.map(r=>getAliasesByRoleDetailed(role)))