parallel and waterfall batch execution

node_batches.js

// parallel batch computation with callback in the end
const parallel = require('async/parallel');
// sequential batch computation with callback in the end
const waterfall = require('async/waterfall');

// all the tasks below run at the same time
function computerParallelBatch(){
  parallel([
    cb=>{
      setTimeout(()=>{
        let val = 1000;
        let error = null;
        cb(error, val);
      },1000);
    },
    cb=>{
      setTimeout(()=>{
        let val = 800;
        let error = null;
        cb(error, val);
      },800);
    },
    cb=>{
      setTimeout(()=>{
        let val = 1500;
        let error = null;
        cb(error, val);
      },1500);
    },
    cb=>{
      setTimeout(()=>{
        let val = 200;
        let error = null;
        cb(error, val);
      },200);
    },
  ],(err,results)=>{
      if(err){
        console.log("some err ", err);
      }else{
        console.log("all results = " + results);
      }
  });
}


function computeAsyncDependentBatch() {
  waterfall([
    // task 1
    cb => {
      setTimeout(() => {
        let val = 300;
        cb(null,val);
      }, 300);
    },
    // task 2 (after task 1 sequential)
    (val,cb)=> {
      setTimeout(() => {
        console.log("previous val : " + val);
        cb(null,[1,2,3,4,5]);
      }, 100);
    }
    // end of tasks, final callback
  ], (err, values) => {
    if(err){
      console.log("error " , err);
    }else{
      console.log("no error " , values);
    }
  });
}


// test 1 - parallel batch
computerParallelBatch();
// test 2 - sequential batch
computeAsyncDependentBatch();