如何从async.js系列返回结果

Question

Every example I see for async.js looks something like this:

var async = require(“async”);
async.series([
  function(callback) {
    setTimeout(function() {
      console.log(“Task 1”);
      callback(null, 1);
    }, 300);
  },
  function(callback) {
    setTimeout(function() {
      console.log(“Task 2”);
      callback(null, 2);
    }, 200);
  },
  function(callback) {
    setTimeout(function() {
      console.log(“Task 3“);
      callback(null, 3);
    }, 100);
  }
], function(error, results) {
  console.log(results);
});

At the end they always just console.log the results. But, how do you actually return the results. Every time I try it just comes back as undefined.

I need something like this:

var async = require('async');

var handler = function()
{
  async.series([
  function(callback) {
    setTimeout(function() {
      console.log('Task 1');
      callback(null, 1);
    }, 300);
  },
  function(callback) {
    setTimeout(function() {
      console.log('Task 2');
      callback(null, 2);
    }, 200);
  },
  function(callback) {
    setTimeout(function() {
      console.log('Task 3');
      callback(null, 3);
    }, 100);
  }
  ], function(error, results) {
    return results;
  });
}

var result = handler();
console.log(result);

But this doesn't work, the result is always undefined.

Ultimately I need to put this up on AWS Lambda and return the results with their context.succeed(results) call. But, I can never get the results. I'm obviously not understanding something about this process, if someone could help it would be much appreciated, thanks!

Answer 1

You can't return result from asynchronous call. What you can do is pass the callback function and when result is available, call that callback function with result as a parameter.

var async = require('async');

var handler = function(cb)
{
  async.series([
  function(callback) {
    setTimeout(function() {
      console.log('Task 1');
      callback(null, 1);
    }, 300);
  },
  function(callback) {
    setTimeout(function() {
      console.log('Task 2');
      callback(null, 2);
    }, 200);
  },
  function(callback) {
    setTimeout(function() {
      console.log('Task 3');
      callback(null, 3);
    }, 100);
  }
  ], function(error, results) {
    cb(error, results)
  });
}

handler(function(err, results) {
  if(!err) {
    console.log(results);
  }
})

Answer 2

try this for async series module

Details: function (req, res) {
    async.series([

    function functionOne(callback) {
            setTimeout(function(err, response) {
            console.log('Task 1');
            callback(null, 1);
            if (err) {
            return callback(err);
            }
            }, 300);
    },

    function functionTwo(callback) {
    setTimeout(function(err, response) {
            console.log('Task 2');
            callback(null, 2);
            if (err) {
            return callback(err);
            }
            }, 200);
    },

    function functionThree(callback) {
    setTimeout(function(err, response) {
            console.log('Task 3');
            callback(null, 3);
            if (err) {
            return callback(err);
            }
            }, 200);

    }
    ], function (err,res) {
    if (err) {
    return res.badRequest(err);
    }
    if (res) {
    return response;
    }

    });
}