The answer of exercise 33 on http://reactive-extensions.github.io/learnrx/

learnrx-exercise33.js

function(sprite, spriteContainer) {
    var spriteMouseDowns = Observable.fromEvent(sprite, "mousedown"),
        spriteContainerMouseMoves = Observable.fromEvent(spriteContainer, "mousemove"),
        spriteContainerMouseUps = Observable.fromEvent(spriteContainer, "mouseup"),
        spriteMouseDrags =
            // For every mouse down event on the sprite...
		spriteMouseDowns.
		    flatMap(function() {
		        return spriteContainerMouseMoves;
		    }).takeUntil(spriteContainerMouseUps);
    
    // For each mouse drag event, move the sprite to the absolute page position.
    spriteMouseDrags.forEach(function(dragPoint) {
        sprite.style.left = dragPoint.pageX + "px";
        sprite.style.top = dragPoint.pageY + "px";
    });
}