graph-scroll.js

Simple scrolling events for d3 graphs. Based on stack

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.

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='sections'>
        <div>Section 0</div>
        <div>Section 1</div>
        <div>Section 2</div>
    </div>

    <div id='graph'></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.

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

With a little bit of css, the graph element snaps to the top of the page while the text scrolls by.

#container{
  position: relative;
  overflow: auto;
}

#sections{
  width: 200px;
  float: left;
}

#graph{
  width: 600px;
  float: left;
  margin-left: 40px;
}

#graph.graph-scroll-fixed{
  position: fixed;
  top: 0px;
  margin-left: 240px;
}

As the bottom of the container approaches the top of the page, the graph is classed with graph-scroll-below. A little more css allows the graph slide out of view gracefully:

#graph.graph-scroll-below{
  position: absolute;
  bottom: 0px;
  margin-left: 240px;
}