Maintaining page view on window resize in a responsive website

Question

Situation:
Suppose we are reading the content somewhere down the page that is built to be responsive. Suppose also that we resize the browser window to a smaller size and that some content above get extended down due to the thinner width, hence making the whole page longer. Then as we resize, whatever content we are looking at will get pushed down the page accordingly.

Example:
Suppose we were to look at the Helper classes section in this page. Then shrinking/expanding the window a sufficient amount moves the bit we were reading down/up the current view.

Prompt:
Is there any way we can fix this? I.e. maintain our current view of the page regardless of what happens to the contents above it when we resize the window.

Thoughts:
I am thinking that we could at least start with javascript and put an event on window resize. Then automatically scroll the page to the top-most element that was in our view on event fire. I don't know how this will affect the performance, however, especially in bigger pages.
There's also the problem of refering to the top-most element in current view. The top of our current view might be cutting off the top portion of some elements, not to mention that there's usually more than 1 element layered on top of one another at any point within the page. The notion of top-most element I've mentioned is not very well-defined :(

Also rather than a problem of responsive design in general, instead it seems to me like this is a problem with the default scrolling behaviour of web browsers? Or perhaps I am missing some circumstances where the current behaviour is desirable.

---

Edit 2 4

Updated fiddle (see fullscreen result) based on Rick Hitchcock's solution's solution.

With jQuery:

//onresize:
var scrollAmount;

if (topNode.getBoundingClientRect().top >= 0) {
    scrollAmount = $(topNode).offset().top - topNode.getBoundingClientRect().top;
} else {
    scrollAmount = $(topNode.offset().bottom - topNode.getBoundingClientRect().bottom;
}
$(window).scrollTop(scrollAmount);

The fiddle is acting a bit weird even in the same browsers, I've uploaded the same script using a free hosting here.
Still need to incorporate the IE, Opera and Safari fix for elementFromPoint.

---

Edit 3

Thanks for all the help, Rick Hitchcock. Welcome to stackoverflow, by the way :)
The discussion is turning into cross-browser compatibility issues so I've accepted your answer since we've pretty much got the answer to the original question. I'll still be fixing up my implementation though. The focus being cross-browser issues, topNode criteria, and topNode cut-off handling.

An edge case

While playing around with it, I noticed that when we were at the bottom of the page in a small viewport, then switch to a larger viewport (let us assume now that some more elements that were originally above the element we saw now came into view due to shorter container from wider viewport) the window cannot always lock the topNode to the top of the viewport in such a case since we've reached the scroll bottom. But then switching back to the small viewport now uses a new topNode that got into the viewport during the switch.
Although this should be expected from the behaviour being implemented, it is still a weird side-effect on scroll bottom.

I will also be looking into this in due course. Initially, I am thinking of simply adding a check for scroll bottom before we update topNode. I.e. to keep the old topNode when we've reached scroll bottom until we've scrolled up again. Not sure how this will turn out yet. I'll make sure to see how Opera handle this as well.

Answer 1

Here's what I've come up with:

(function(){
   var topNode;

   window.onscroll=function() {
     var timer;
     (function(){
        clearTimeout(timer);
        timer= setTimeout(
                 function() {
                   var testNode;
                   topNode= null;
                   for(var x = 0 ; x < document.body.offsetWidth ; x++) {
                     testNode= document.elementFromPoint(x,2);
                     if(!topNode || testNode.offsetTop>topNode.offsetTop) {
                       topNode = testNode;
                     }
                   }
                 },
                 100
               )
      }
     )();
   }

   window.onresize=function() {
     var timer;
     (function(){
        clearTimeout(timer);
        if(topNode) {
          timer= setTimeout(function(){topNode.scrollIntoView(true)},10);
        }
      }
     )();
   }
 }
)();

If there were a window.onbeforeresize() function, this would be more straightforward.

Note that this doesn't take into account the scrolled position of the element's textNode. We could handle that if only the height of the window were resized. But resizing the width would generally cause reformatting.

This works in Chrome, Firefox, IE, and Safari.

Edit

How it works

The code's closures make variables private, and the timers prevent the code from running constantly during scrolling/resizing. But both tend to obfuscate the code, so here's another version, which may aid in understanding. Note that the onscroll timer is required in IE, because elementFromPoint returns null when it used in onscroll event.

var topNode;

window.onscroll=function() {
  setTimeout(
    function() {
      var testNode;
      topNode= null;
      for(var x = 0 ; x < document.body.offsetWidth ; x++) {
        testNode= document.elementFromPoint(x,2);
        if(!topNode || testNode.offsetTop>topNode.offsetTop) {
          topNode = testNode;
        }
      }
    },
    100
  )
}

window.onresize=function() {
  if(topNode) {
    topNode.scrollIntoView(true)
  }
}

topNode maintains the screen's top-most element as the window scrolls.

The function scans the screen left to right, along the 3rd row: document.elementFromPoint(x,2)*

It doesn't scan along the 1st row, because when IE does scrollIntoView, it pushes the element down a couple pixels, making the top-most screen element the previous element. (Figured this out through trial and error.)

When the window is resized, it simply positions topNode at the top of the screen.

[*Originally, onscroll scanned left to right along the 11th row (in pixels) until it found an element with just one child. The child would often be a textNode, but that wouldn't always be the case. Example:

<div><ul><li>...<li>...<li>...</ul></div>

The div has only one child – the ul. If the window were scrolled to the 50th li, scanning left to right would incorrectly return the div due to the inherent padding of lis.

The original code has been updated. ]