当.then以正确的顺序执行时，如何使javascript函数起作用。

Question

I've read many posts on this topic and think I should be using $.when and .then or .done for what I need, but not sure how to make it happen. Any help you can provide is appreciated.

I have two functions that can run simultaneously, and a third function that can only run after the first two are complete. Here's a basic breakdown of what I'm doing.

function one() {
  //do lots of stuff to get variable values set
  return $.post("sess_push.php", {hotel:hotel, hlng:hLng, hlat:hLat})
            .done(function( data ) {
            console.log("Done in function one");
            alert( "Done in function one" );
        });
} //end function one

function two() {
  //do lots of stuff to get variable values set
  return $.post("sess_push.php", {metro:metro, lat:lat, lng:lng})
        .done(function( data ) {
        console.log("Done with function 2");
        alert ("Done with function 2");
    });
} //end function two

function three() {
    console.log("Starting function 3");
        alert("Starting function 3");
        $.post("itenerary.php", {})
        .done(function( data ) {
          $("#itenerary").html(data);
        });
} // end function three

How do I use promises and/or deferred to get these to execute in the order I need?

I've tried to use the following $.when, but function three runs before the other two are done. $.when(one(), two()).then( three, myFailure );

Answer 1

I'm sure there are better ways to make this work, but this is what did the trick for me. Thanks to Jaromanda X for providing the base for what I used to get it working. if others have ways to optimize this, I'm all for it.

function one() {
  var d = $.Deferred();
  //do lots of stuff to get variable values set

  $.post("sess_push.php", {hotel:hotel, hlng:hLng, hlat:hLat});
  console.log("Done in one");
  d.resolve();
  return d.promise();
} //end function one

function two() {
  var d = $.Deferred();
  //do lots of stuff to get variable values set

  $.post("sess_push.php", {metro:metro, lat:lat, lng:lng});
  console.log("Done with two");
  d.resolve();
  return d.promise();
} //end function two

function three() {
    var d = $.Deferred();
    $.post("itenerary.php", {})
    .done(function( data ) {
        $("#itenerary").html(data);
    console.log("Done in 3");
    });
    d.resolve();
    return d.promise();

} // end function three