Script to be pasted into developer tools to log calls to programmatic scrolling APIs. Currently tested just on Chrome and Firefox.

Logging programattic scrolls

(function(){
  // Override function in given prototype to add a log statement 
  function logMethod(prototype, fname) {
    var name = prototype.constructor.name + '.' + fname;
    if (!(fname in prototype)) {
      console.warn("Warning: can't instrument " + name);
      return;
    }
    console.log("Instrumenting " + name);
    var original =  prototype[fname];
    
    prototype[fname] = function() {
      // Want single line output but with optional callstack - abuse 'error' for this.
      // console.trace is also good but expands the callstack by default.'
      console.error(name + ' invoked with ' + JSON.stringify(Array.prototype.slice.call(arguments)));
      // debugger;
      original.apply(this, arguments);
    };
  }
  
  // Override property setter to add a log statement
  function logSetter(prototype, property, errContext) {
    var name = prototype.constructor.name + '.' + property;
    var original = Object.getOwnPropertyDescriptor(prototype, property);
    if (!original) {
      console.warn("Warning: can't instrument " + name + '. ' + errContext);
      return;
    }
    console.log("Instrumenting " + name);
    
    Object.defineProperty(prototype, property, {
      set: function(v) {
        var changed = v !== original.get.call(this);
        console.error(name + ' set to:' + v + (changed?' (changed)':' (not changed)')); // add changed indicator
        // debugger;
        original.set.call(this, v);
      },
      get: original.get
    });
  }
  
  var win = window;
  // Work around for http://crbug.com/475587
  if ('scrollBy' in window && !window.hasOwnProperty('scrollBy'))
    win = Window.prototype;

  for (var m of ['scrollBy', 'scrollTo', 'scroll'])
    logMethod(win, m);

  for (var m of ['scrollIntoView', 'scrollIntoViewIfNeeded', 'focus'])
    if (m in Element.prototype)
      logMethod(Element.prototype, m);
  
  for (var p of ['scrollTop', 'scrollLeft'])
    logSetter(Element.prototype, p, "Chrome 43+ required (http://crbug.com/43394)");
})();