How to disable scrolling temporarily?

The scroll event cannot be canceled. But you can do it by canceling these interaction events:
Mouse & Touch scroll and Buttons associated with scrolling.

[Working demo]

// left: 37, up: 38, right: 39, down: 40,
// spacebar: 32, pageup: 33, pagedown: 34, end: 35, home: 36
var keys = {37: 1, 38: 1, 39: 1, 40: 1};

function preventDefault(e) {
  e.preventDefault();
}

function preventDefaultForScrollKeys(e) {
  if (keys[e.keyCode]) {
    preventDefault(e);
    return false;
  }
}

// modern Chrome requires { passive: false } when adding event
var supportsPassive = false;
try {
  window.addEventListener("test", null, Object.defineProperty({}, 'passive', {
    get: function () { supportsPassive = true; } 
  }));
} catch(e) {}

var wheelOpt = supportsPassive ? { passive: false } : false;
var wheelEvent = 'onwheel' in document.createElement('div') ? 'wheel' : 'mousewheel';

// call this to Disable
function disableScroll() {
  window.addEventListener('DOMMouseScroll', preventDefault, false); // older FF
  window.addEventListener(wheelEvent, preventDefault, wheelOpt); // modern desktop
  window.addEventListener('touchmove', preventDefault, wheelOpt); // mobile
  window.addEventListener('keydown', preventDefaultForScrollKeys, false);
}

// call this to Enable
function enableScroll() {
  window.removeEventListener('DOMMouseScroll', preventDefault, false);
  window.removeEventListener(wheelEvent, preventDefault, wheelOpt); 
  window.removeEventListener('touchmove', preventDefault, wheelOpt);
  window.removeEventListener('keydown', preventDefaultForScrollKeys, false);
}

UPDATE: fixed Chrome desktop and modern mobile browsers with passive listeners

Do it simply by adding a class to the body:

.stop-scrolling {
  height: 100%;
  overflow: hidden;
}

Add the class then remove when you want to re-enable scrolling, tested in IE, FF, Safari and Chrome.

$('body').addClass('stop-scrolling')

---

For mobile devices, you'll need to handle the touchmove event:

$('body').bind('touchmove', function(e){e.preventDefault()})

And unbind to re-enable scrolling. Tested in iOS6 and Android 2.3.3

$('body').unbind('touchmove')