Odd behaviour on initial scroll in Chrome

smartscroll

smartscroll is a tiny (1815b minfied + gzipped) jQuery plugin that has these independent features:

Section scrolling - Scrolljacking
Auto-hash - Updates the URL hash based on current position on page
Responsive - You can disable scrolljacking below a set breakpoint

It also supports:

Varied Section Heights
Hybrid Scrolling - Both normal and scrolljacking on the same page
Compatible with scrollbar - Can use scrollbar as well as mousewheel
Disabling permalink history
Correctly detects scroll events for inertial scrolling, by integrating with lethargy as a soft dependency (which means it will work without it)
Provides events you can listen to, by integrating with EventEmitter as a soft dependency

Demo

Requirements

There can only be one set of adjoining sections

How to Use

Install lethargy, which is available as a Bower package, which you can install with bower install.

Structure your HTML like so (default options included)

<body>
  <div class="section-wrapper">
    <div class="section" data-hash="section-hash-name"></div>
    <div class="section" data-hash="section-hash-name"></div>
  </div>
<script src="path/to/lethargy.min.js">
<script src="https://rawgit.com/Olical/EventEmitter/master/EventEmitter.min.js"></script>
<script src="path/to/smartscroll.min.js">
<script>
  var options = {
    mode: "vp", // "vp", "set"
    autoHash: false,
    sectionScroll: true,
    initialScroll: true,
    keepHistory: false,
    sectionWrapperSelector: ".section-wrapper",
    sectionClass: "section",
    animationSpeed: 300,
    headerHash: "header",
    breakpoint: null,
    eventEmitter: null,
    dynamicHeight: false
  };
  $.smartscroll(options);
</script>
</body>

You may also want to link to styles.css, but all that does is to ensure the html and body elements have no margins nor padding

You may also leave out lethargy, but smartscroll may not work as well with scroll devices that uses inertial scrolling. Performance with lethargy can be slower, but it will be improved with further development.

Options

mode - (String) Valid options are:
- vp (Viewport) - The sections will be automatically sized to be the same as the viewport
- set - Use the height and width set by CSS (use this for having different heights for different sections)
autoHash - (Boolean) Whether the auto-hashing feature is enabled. If you use this feature, it is important to use EventEmitter as well, otherwise smartscroll will listen to every scroll event, which is very resource-draining and can make the animation more 'glitchy'
sectionScroll - (Boolean) Whether the section-scrolling feature is enabled
initialScroll - (Boolean) Whether smartscroll should scroll to the position specified by the hash on initial load
keepHistory - (Boolean) Whether scrolling through different sections will be recorded in the browser's history
sectionWrapperSelector - (String) The CSS selector for the block element which wraps around your sections
sectionClass - (String) The class name applied to each section
animationSpeed - (Integer) Time taken for the scroll animation, in miliseconds
headerHash - (String) The hash for the section above the sections, must be non-empty to reliably ensure the page do not jump when updating the hash value across browsers (as # means _top)
breakpoint - (Integer) The width of the browser below which scrolljacking will be disabled
sectionSelector - (String) The selector applied to each section, overrides sectionClass and allow more flexibility in choosing a selector. (Added in 2.1.0)
dynamicHeight - (Boolean) If you are going to be dynamically adding and removing content so as to change the position and/or size of the section wrappers and/or sections, then set this to true. Set to false otherwise to increase performance.
eventEmitter - (Object) If you pass in an EventEmitter object, autoHashing will be much more efficient. You can also listen to the scroll events this way. Defaults to null.
ie8 - If you need to support Internet Explorer 8, change this to true. Defaults to false.
bindSwipe - (Boolean) Allow for listening of swipe events. Requires EventEmitter. Defaults to true
bindKeyboard - (Boolean) Allow for keyboard events (up and down arrows) to control slides. Defaults to true

Events

Smartscroll has a soft dependency on EventEmitter. If present, smartscroll can provide six events scrollStart, scrollEnd, swipeLeft, swipeRight, swipeDown and swipeUp. The scrollStart and scrollEnd listener will receive the slide number as its only argument; the first slide will have a number of 1, the section before the sectionWrapper will have a number of 0.

var ee = new EventEmitter();
var scrollStartListener = function (slideNumber) {
  console.log("Scrolling to " + slideNumber);
}
var scrollEndListener = function () {
  console.log("Scrolling End");
}
ee.addListener('scrollStart', scrollStartListener);
ee.addListener('scrollEnd', scrollEndListener);
$.smartscroll({
  ...
  eventEmitter: ee
});

The other listeners receive no arguments.

var ee = new EventEmitter();
var swipeUpListener = function () {
  console.log("Swiping Up");
}
var swipeDownListener = function () {
  console.log("Swiping Down");
}
$.smartscroll({
  ...
  eventEmitter: ee,
  bindSwipe: true
});
ee.addListener('swipeUp', swipeUpListener);
ee.addListener('swipeDown', swipeDownListener);

Manual Scroll

You can manually scroll up or scroll down.

When you first initiate smartscroll with $.smartscroll(), it returns an object. In that object is the scroll function, which is called with a single parameter. If the parameter is truthy, it will scroll down, otherwise, it will scroll up.

var smartscroll = $.smartscroll();
smartscroll.scroll(1);

Architecture

Currently, there are two features of smartscroll, and this is how it's implemented:

Smooth scroll by section

The mousewheel and DOMMouseScroll (for Firefox) events are bound.

When such event is fired in vp mode, smartscroll will find it's most prominent section (one which occupies most of the screen), and smoothly scroll to the section above or below it.

When the event is fired in set mode, smartscroll will find which section occupies the middle of the screen, and smoothly scroll to the section above or below it.

When scrolling outside of the sections, normal scrolling resumes.

Changing URL hash based on the current section

The scroll event is bound.

When the event is fired in vp mode, smartscroll will see which section occupies the top of the viewport, and if the hash is different, replace it with the new one.

When the event is fired in set mode, smartscroll will see which section occupies the middle of the viewport, and if the hash is different, replace it with the new one.