What is the proper method for determining the height of a scrollbar's grip?

Have you ever noticed that Facebook has a unique component on the right-most column? When the browser window is maximized, it looks like this:

But when you resize your browser window to be smaller, it changes to this:

The grip within the overflowing container also resizes along with the rest of the components. This allows for easy scrolling down to the bottom element inside the container.

A similar component can be created using jQuery-Ui:

However, the challenge lies in calculating the new grip size when the container is resized:

Although progress has been made, the grip still needs to be adjusted to enable smooth scrolling to the bottom, just like the one seen on Facebook.

So, the question remains: what formula should be used to achieve this?

Here’s an attempt at a calculation function:

function calculate_grip_size() { 
  h = (parseFloat($('#box-container').css('height')) / parseFloat($('#box').css('height')))*100; 
  $('#grip').css('height', h);  
} 

And here is the corresponding HTML code:

<div id="box-container">
  <div id="area-track">
    <div id="grip">
    </div>
  </div>
  <div id="box">
    <div class="ipsum"> Lorem ipsum... </div>
    <div class="ipsum"> Lorem ipsum... </div>
    <div class="ipsum"> Lorem ipsum... </div>
    <div class="ipsum"> Lorem ipsum... </div>
    <div class="ipsum"> Lorem ipsum... </div>
    <div class="ipsum"> Lorem ipsum </div> 
  </div>
</div>

Answer №1

Explore the inner workings of a scrollbar.

The size of the grip on a scrollbar is determined by a calculation involving a multiplication factor and a content ratio. For example, if your content is 200px and the outer box is 100px, the ratio would be 2.0. As the content grows larger, the grip size will decrease proportionally, so it's important to establish a minimum value for it.

The multiplication factor is a customizable number that allows you to adjust the appearance of the scrollbar to ensure it looks visually appealing at all scales.

Answer №2

Recently, I came across a plugin called slimScroll and the developer shared an interesting method that can be adapted to suit your needs by using class names instead of IDs for better generalization:

var minH = 50,
    h = Math.max( $('.box-container').outerHeight() / parseInt($('.box').prop('scrollHeight'),10) * 100, minH );
$('.grip').height(h);

Update: I made a mistake in my calculations and forgot to parse the scrollHeight value. Make sure to correct it.

Update #2: After further investigation, I noticed two issues:

  1. The initial calculation didn't consider that the grip was within the area-track, which has a different height compared to the box-container

    $('.grip').height($('#area-track').height() * h);
    
  2. The content was positioned with a 1:1 ratio with the grip, so it required division by the content ratio

    increment = parseInt(ui.helper.css('top')) / -h;
    

Feel free to check out the demo I created based on the code you provided.

Additionally, I had to include padding-bottom: 25px; in the CSS definition for .box to ensure the entire content box was visible - adjust this as necessary depending on the padding present.

Answer №3

Instead of using the .css('height') method, opt for using .height(). The latter will provide you with the actual calculated height of the element, rather than just returning the css value.

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