github.com/1wheel/graph-scroll

graph-scroll.js

Simple scrolling events for d3 graphs. Based on stack

Demo/Documentation

graph-scroll takes a selection of explanatory text sections and dispatches active events as different sections are scrolled into to view. These active events can be used to update a chart's state.

d3.graphScroll()
    .sections(d3.selectAll('#sections > div'))
    .on('active', function(i){ console.log(i + 'th section active') })

The top most element scrolled fully into view is classed graph-scroll-active. This makes it easy to highlight the active section with css:

#sections > div{
	opacity: .3
} 

#sections div.graph-scroll-active{
	opacity: 1;
}

To support headers and intro images/text, we use a container element containing the explanatory text and graph.

<h1>Page Title</div>
<div id='container'>
  <div id='graph'></div>
  <div id='sections'>
    <div>Section 0</div>
    <div>Section 1</div>
    <div>Section 2</div>
  </div>
</div>
<h1>Footer</h1>

If these elements are passed to graphScroll as selections with container and graph, every element in the graph selection will be classed graph-scroll-graph if the top of the container is out of view.

d3.graphScroll()
	.graph(d3.selectAll('#graph'))
	.container(d3.select('#container'))
  .sections(d3.selectAll('#sections > div'))
  .on('active', function(i){ console.log(i + 'th section active') })

When the graph starts to scroll out of view, position: sticky keeps the graph element stuck to the top of the page while the text scrolls by.

#container{
  position: relative;
}

#sections{
  width: 340px;
}

#graph{
  margin-left: 40px;
  width: 500px;
  position: sticky;
  top: 0px;
  float: right;
}

On mobile centering the graph and sections while adding a some padding for the first slide is a good option:

@media (max-width: 925px)  {
  #graph{
    width: 100%;
    margin-left: 0px;
    float: none;
  }

  #sections{
    position: relative;
    margin: 0px auto;
    padding-top: 400px;
  }
}

Adjust the amount of pixels before a new section is triggered is also helpful on mobile (Defaults to 200 pixels):

graphScroll.offset(300)

To update or replace a graphScroll instance, pass a string to eventId to remove the old event listeners:

graphScroll.eventId('uniqueId1')