bl.ocks.org - lots of D3 examples. Search Gist for examples or search in Google using the site: operator ("site:bl.ocks.org").
<script src="https://d3js.org/d3.v4.min.js"></script> <script>var svg = d3.select("svg") .style("width","100%") .style("height","100%");
svg.append("circle") .attr("cx",100) .attr("cy",200) .style("fill","blue") .attr("r",50);
svg.append("circle") .attr("cx",500) .attr("cy",200) .style("fill","red") .attr("r",20);
</script>