Or you can make a count-down latch of some kind:

  var num_results = 3;
  var results = []
  var makeCallback = function(index) {
    return function(response) {
      num_results -= 1;
      results[index] = response;
      if (num_results > 0) {
        return;
      }
      
      // actually do stuff here, all results are loaded.
    };
  };
  $.get("/a", makeCallback(0));
  $.get("/b", makeCallback(1));
  $.get("/c", makeCallback(2));
  // etc

It's also not hard to make a generic latch-producing function so you can just write stuff like:

  var l = makeLatch(callback);
  $.get("/a", l());
  $.get("/b", l());
  $.get("/c", l());