如何确保节点js在进行异步调用后返回数据？

Question

I was asked this question in an interview today that say node.js is used to make 3 REST webservice calls. The calls are independent and so you can make them in parallel. However towards the end of the method, you need to wait for all the webservice calls to return result. You need to collate all the results and send it back.

I said that I will chain the promises and return the result only from the resolve of the third promise. However, the interviewer was not satisfied with the answer. I am not sure if there is anything I missed. Please let me know.

EDIT : I have added the below notes to explain my solution.

My solution was -

var p1 = new Promise() // From here to make the first call
var p2 = new Promise() // Second Call
var p3 = new Promise() //Third Call

p1.resolve(p2.resolve()).p3.resolve( return result)

I thought that this way we would block the call until the data from all the three services are retrieved.

Answer 1

I use the Promise.all() method to verify that all promises were succesfully resolved.

The Promise.all() method returns a single Promise that resolves when all of the promises in the iterable argument have resolved, or rejects with the reason of the first promise that rejects.

MDN Reference, For More Info

Example:

The webServicePromises in the example below would be an array of promises.

  Promise.all(webServicePromises).then((responses) => {
        for(let i = 0; i< responses.length; i++){
           let response = responses[i];
           //do stuff with each web service response
        }
        },  reason => {
            console.log(reason);
        }).catch(error => logError(`${error}`));

Answer 2

Try using this package.

async.parallel({
    one: function(callback) {
        setTimeout(function() {
            callback(null, 1);
        }, 200);
    },
    two: function(callback) {
        setTimeout(function() {
            callback(null, 2);
        }, 100);
    },
    three: function(callback) {
        setTimeout(function() {
            callback(null, 3);
        }, 50);
    }
}, function(err, results) {
    // results is now equals to: {one: 1, two: 2, three: 3}
});

Above example is aync package's parallel api, it has many more. If you are working on node then this library is quite handly.

Let me know in case any doubt.

Thanks!