JSFiddle - React, Tailwind, and code Playground

HTML

<h2>This should update twice</h2>
<p>But it only updates once</p>
<div id="demo"></div>

CSS

body { font-family: sans-serif; }
path { stroke: purple; stroke-width: 2px; fill: none; }

JavaScript

var chart = demoChart();
var pts = [[[0,0],[200,0.25],[500,1]]];

console.log("");
d3.select("#demo").datum(pts).call(chart);

setTimeout(function() {
    console.log("Modifying data array");
    pts[0][1][1] = 0.5;
    d3.select("#demo").datum(pts).call(chart);
},1000);

setTimeout(function() {
    console.log("Passing new data array (doesn't work)");
    d3.select("#demo")
    .datum([[[0,1],[200,0.45],[500,0]]])
    .call(chart);
},1000);


function demoChart() {
	
	function xs(d) { return xScale(d[0]) }
	function ys(d) { return yScale(d[1]) }

	var xScale = d3.scale.linear().domain([0, 500]).range([0, 400]),
		yScale = d3.scale.linear().domain([0, 1]).range([400, 0]),
		line = d3.svg.line().x(xs).y(ys);

	function chart(selection) {
		selection.each(function(data) {
			console.log("passed data: ", data);

			// Select the svg element, if it exists; otherwise create it
			var svg = d3.select(this).selectAll("svg").data([1]);
			var svgGEnter = svg.enter().append("svg").append("g");

			// Select/create/remove plots for each y, with the data
			var plots = svg.select("g").selectAll(".plot").data(data);
			plots.exit().remove();
			var plotsEnter = plots.enter().append("g").attr("class","plot");
			plotsEnter.append("path");

			// Update the line paths
			plots.selectAll("path")
				.transition()
					.attr("d", function(d,i) {
						console.log("transitioning line with data: ", d);
						return line.apply(this, arguments);
					});

			svg.attr("width", 400).attr("height", 400);
		});
	}
    
	return chart;
}