I want to launch a series of async tasks without using Promise & Async await. My worfklow is : . task 1 . task 2 . task 3 & 4 (in parallel)

I've tried the library async for that. That's ok for a series of sequential task or a series of parallel. But to implement my worklfow, I'm stuck for the moment.

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

const readFile1 = (name, callback) => {
        fs.readFile(name, 'utf-8', (err, data) => {
                if (err) {
                        callback(err);
                }
                console.log(data);
                callback(null, data);
        });
}

async.series([
function(callback1) {
        async.series([
                function(callback1) {
                        readFile1('./1.txt', callback1);
                },
                function(callback1) {
                        readFile1('./2.txt', callback1);
                },
        ], function(err, results) {
                console.log('series ', results);
        });
},
function(callback2) {
        async.parallel([
                function(callback2) {
                        readFile1('./3.txt', callback2);
                },
                function(callback2) {
                        readFile1('./4.txt', callback2);
                },
        ], function(err, results) {
                console.log('parallel ', results);
        });
}
]);

For now only the step 1 & 2 are executed. Have you got an idea for this (apart using a more modern code style with async / await & promises?)

Blured

CodePudding user response：

You need to call the top-level callbacks before async.series() will continue to the next step:

async.series([
  function (callback) {
    async.series(
      [
        function (callback1) {
          readFile1("./1.txt", callback1);
        },
        function (callback2) {
          readFile1("./2.txt", callback2);
        },
      ],
      function (err, results) {
        console.log("series ", results);
        return callback(err, results); // <-- here
      }
    );
  },
  function (callback) {
    async.parallel(
      [
        function (callback1) {
          readFile1("./3.txt", callback1);
        },
        function (callback2) {
          readFile1("./4.txt", callback2);
        },
      ],
      function (err, results) {
        console.log("parallel ", results);
        return callback(err, results); // <-- and here
      }
    );
  },
]);

(renamed callback names to make things a bit more clear)