javascript - What's the difference between a continuation and a callback?

Question

I've been browsing all over the web in search of enlightenment about continuations, and it's mind boggling how the simplest of explanations can so utterly confound a JavaScript programmer like myself. This is especially true when most articles explain continuations with code in Scheme or use monads.

Now that I finally think I've understood the essence of continuations I wanted to know whether what I do know is actually the truth. If what I think is true is not actually true, then it's ignorance and not enlightenment.

So, here's what I know:

In almost all languages functions explicitly return values (and control) to their caller. For example:

var sum = add(2, 3);

console.log(sum);

function add(x, y) {
    return x + y;
}

Answer 1

I believe that continuations are a special case of callbacks. A function may callback any number of functions, any number of times. For example:

var array = [1, 2, 3];

forEach(array, function (element, array, index) {
    array[index] = 2 * element;
});

console.log(array);

function forEach(array, callback) {
    var length = array.length;
    for (var i = 0; i < length; i++)
        callback(array[i], array, i);
}