如何并行运行API调用（Node.js）

Question

I am trying to run some API calls in parallel, but am having problems since I am trying to call a function again before the API data has been returned.

I am thinking that I could possibly use the new command in Node, but am not sure how to structure it into this scheme. I am trying to avoid recursion, as I already have a recursive version working and it is slow.

Currently I am trying to this code on the server.

loopThroughArray(req, res) { 
  for(let i=0; i<req.map.length; i++) {
    stack[i] = (callback) => {
      let data = getApi(req, res, req.map[i], callback)
    }
  }

  async.parallel(stack, (result) => {
      res.json(result)
  })
}

....

function getApi(req, res, num, cb) {
  request({
    url: 'https://example.com/api/' + num
  },
  (error, response, body) => {
    if(error) {
      // Log error
    } else {
      let i = {
        name: JSON.parse(body)['name'],
        age: '100'
      }
      console.log(body) // Returns empty value array.length > 1 (req.map[i])
      cb(i)
    }
  })

Is there a way to spawn new instances of the function each time it's called and accumulate the results to send back as one result to the client?

Answer 1

Here's an example of calling Web APIs (each with different parameters), using the Async library, we start by creating an array of N function variables.

const async = require('async');
const request = require('request');

//Set whatever request options you like, see: https://github.com/request/request#requestoptions-callback
var requestArray = [
    {url: 'https://httpbin.org/get'},
    {url: 'https://httpbin.org/ip'}
];

let getApi = function (opt, callback) {
    request(opt, (err, response, body) => {
        callback(err, JSON.parse(body));
    });
};

const functionArray = requestArray.map((opt) => { 
    return (callback) => getApi(opt, callback); 
});

async.parallel(
    functionArray, (err, results) => {
        if (err) {
            console.error('Error: ', err);
        } else {
            console.log('Results: ', results.length, results);
        }
});

You can easily switch the Url and Query values to match whatever you need. I'm using HttpBin here, since it's good for illustrative purposes.