JSFiddle - React, Tailwind, and code Playground

JavaScript

var resultData = "result-data-string";

// Create a jQuery deferred
defA = $.Deferred();

// Make an ajax call, which creates a jqXHR object
defB = $.ajax({
  type: "POST",
  url: "/echo/json/",
  data: {
    json: JSON.stringify(resultData),
    delay: 1.5
  }
});

defA.done(function(data) {
  console.log("defA resolved");
  console.log(data);
  // data is resultData, as expected
});

defB.done(function(data) {
  console.log("defB resolved");
  console.log(data);
  // data is resultData, as expected
});


defAB = $.when(defA, defB);

defAB.done(function(aData, bData) {
  console.log("defAB resolved");
  console.log(aData);
  // aData is resultData, as expected
  console.log(bData);
  // aData is an array for some reason:
  // [ resultData, "success", jqXHR object? 
});

defA.resolve(resultData);