line_Transition_4

<!DOCTYPE html>
<head>
  <meta charset="utf-8">
  <script src="https://d3js.org/d3.v4.min.js"></script>

</head>

<body>
  <script>
var n = 243,
    duration = 750,
    now = new Date(Date.now() - duration),
    count = 0,
    random = d3.randomNormal(0, .2),
    data = d3.range(n).map(random);

var margin = {top: 6, right: 0, bottom: 20, left: 40},
    width = 960 - margin.right,
    height = 120 - margin.top - margin.bottom;

var x = d3.scaleTime()
    .domain([now - (n - 2) * duration, now - duration])
    .range([0, width]);

var y = d3.scaleLinear()
    .range([height, 0]);

var line = d3.line()
//     .interpolate("basis")
    .x(function(d, i) { return x(now - (n - 1 - i) * duration); })
    .y(function(d, i) { return y(d); });

var svg = d3.select("body").append("p").append("svg")
    .attr("width", width + margin.left + margin.right)
    .attr("height", height + margin.top + margin.bottom)
    .style("margin-left", -margin.left + "px")
  .append("g")
    .attr("transform", "translate(" + margin.left + "," + margin.top + ")");

svg.append("defs").append("clipPath")
    .attr("id", "clip")
  .append("rect")
    .attr("width", width)
    .attr("height", height);

var axis = svg.append("g")
    .attr("class", "x axis")
    .attr("transform", "translate(0," + height + ")")
    .call(x.axis = d3.axisBottom(x));

var path = svg.append("g")
    .attr("clip-path", "url(#clip)") 
  .append("path")
    .datum(data)
    .attr("class", "line");

var transition = d3.select({}).transition()
    .duration(750)
    .ease(d3.easeLinear);

d3.select(window)
    .on("scroll", function() { ++count; });

path
  .transition()
    .duration(500)
    .ease(d3.easeLinear)
    .on("start", tick);    
    
function tick() {

// update the domains
    now = new Date();
    x.domain([now - (n - 2) * duration, now - duration]);
    y.domain([0, d3.max(data)]);

// push the accumulated count onto the back, and reset the count
    data.push(Math.min(30, count));
    count = 0;

// redraw the line 
    svg.select(".line")
        .attr("d", line)
        .attr("transform", null);

// slide the x-axis left
    axis.call(x.axis);

// slide the line left
    path.transition()
        .attr("transform", "translate(" + x(now - (n - 1) * duration) + ")");

// pop the old data point off the front
    data.shift();

};

</script>
</body>

https://d3js.org/d3.v4.min.js