node step module example using `parallel()`

step-with-parallel-example.js

var Step = require("step");

function asyncFn(str, cb) {
  setTimeout(function() {
    let err = null;
    let result = " Hello " + str;
    return cb(err, result); // error-first style callback
  }, 1000);
}

// Step executes async functions synchronously
Step(
  // Step1:
  function() {
    console.log("step1:");
    asyncFn("hoge", this);
  },
  // Step2:
  function(err, result) {
    console.log("step2:");
    console.log(" err=", err, ", result=", result);
    if (err) throw err;
    //  *** passing 2nd arg of next function
    asyncFn("foo", this.parallel());
    //  *** passing 3rd arg of next function
    (function(_p, cb) {
      return cb(null, _p);
    })("Hello baa", this.parallel());
    //  *** passing 4th arg of next function
    asyncFn("baz", this.parallel());
  },
  // Step3:
  function(err, result1, result2, result3) {
    console.log("step3:");
    if (err) throw err;
    console.log(" err=", err, ", result1=", result1, ", result2=", result2,", result3=", result3);
  });

/* 
### Result:

step1:
step2:
 err= null , result=  Hello hoge
step3:
 err= undefined , result1=  Hello foo , result2= Hello baa , result3=  Hello baz
*/