Synchronous iteration for milding cpu overload using node-step with generator

step-with-generator.js

const Step = require("step");

Step(
  //
  // ** 1st Step:
  //
  function() {
    console.log("### 1st Step:");
    let arr = ["aaa", "bbb", "ccc"];
    let err, result;
    // Iter:
    let ite = function*(cb) {
      for (let len = arr.length, i = 0; i < len; i++) {
        console.log("ite: waiting for `next()`...");
        yield toUpper(i);
      };
      err = null;// error is null if ok
      result = arr; // sets upperCased strings as result
      cb(err, result);
    }(this); // to the next step
    // first fire!
    ite.next();
    // Any fn to be executed in above generator:
    function toUpper(idx) {
      setTimeout(function() {
        console.log(` toUpper: ${arr[idx]} => ${arr[idx].toUpperCase()}`);
        arr[idx] = arr[idx].toUpperCase();
        console.log(" toUpper: doing next()");
        arr[idx] = arr[idx].toUpperCase();
        return ite.next();
      }, 1000);
    }
  },
  //
  // ** 2nd Step:
  //
  function(err, result) {
    if(err) throw err;
    console.log("### 2nd Step:");
    console.log(`err:${err}, result:${result}`);
  });

// Result:
//
// ### 1st Step:
// ite: waiting for `next()`...
//  toUpper: aaa => AAA
//  toUpper: doing next()
// ite: waiting for `next()`...
//  toUpper: bbb => BBB
//  toUpper: doing next()
// ite: waiting for `next()`...
//  toUpper: ccc => CCC
//  toUpper: doing next()
// ### 2nd Step:
// err:null, result:AAA,BBB,CCC