fixed typo in $.each statement. (otherwise each url will be a numeral: 0,1,2..)

parallel.js

var results = {};
var requests = 0;

var urls = ["values/1", "values/2", "values/3"];

$.each(urls, function(idx, url) {
  $.getJSON(url, function(data) {
    results[url] = data.value;
    ++requests;


    if (requests == 3) {
      $('#mynode').html( results[urls[0]] / results[urls[1]] * results[urls[2]]);
    }
  });
});

      

serial.js

$.getJSON("/values/1", function(data) {
  // data = {value: 1}
  var value_1 = data.value;

  $.getJSON("/values/2", function(data) {
    // data = {value: 42}
    var value_2 = data.value;

    var sum = value_1 + value_2;

    $('#mynode').html(sum);
  });

});