Mixing sync and async javascript/jquery and getting a success function at the end

Wondering what the best solution to this problem is, also this is not my actual code structure or names but the simplest way to illustrate the problem. I have a function which was purely used to perform an ajax call and load a template with jquery.

function load(template) {
    $('#container').load(template, data, function() {
       // complete code here
    }); 
}

Focusing on the 3rd param in $.load(), namely a callback function that runs when the request is complete.

Now I have my load() function in another wrapper function:

function processTask(variable) {
    load(variable);
}

The problem I have is I need some code to run after the ajax load is complete, however as my app has grown my wrapper function processTask may or may not invoke an ajax load so I can't perform my must needed code inside the complete callback.

Do I change my $.load() to perform synchronous or just manage my code better so that if I am calling a $.load() it puts my needed code in the callback and if not it places it where I need it to be?

I have read about javascript Promises and I'm unsure if they will help in this situation.

EDIT

So my processTask is an object method.

function classObj(name, fn) {
    this.name = name;
    this.processTask = fn;
    this.load = function(template) {
        $('#container').load(template, data, function() {
           // complete code here
        });
    }
}

And in context I do this:

var task = new classObj('taskName', function() {  
    this.load('myFile.php'); 
    // Or another function and not load() based on whats needed in the task. 
});

Basically I have an object that I can add custom methods to at will and they can easily be called dynamically, until now they have always loaded a file.

First, change your load function to return the xhr from get (or ajax):

function load(template) {
    return $.get('myFile.php', data, function(result) {
       $('#container').html(result);
    }); 
}

Then, within your code you can use whenthen to perform your code after the load completes if applicable:

var xhr;

/* ... */

if(something){
     xhr = load(template);
}

/* ... */

if(xhr){
    $.when(xhr).then(doSomething);
} else {
    doSomething();
}

And in fact, this can be simplified using the fact that a non-deferred object passed to when (including undefined apparently) will execute the then immediately and get rid of the if:

$.when(xhr).then(doSomething);

If xhr is undefined then when will resolve immediately causing then to execute immediately.