data types

<!DOCTYPE html>
<head>
  <meta charset="utf-8">
  <script src="https://d3js.org/d3.v4.min.js"></script>
  <style>
    body { margin:0;position:fixed;top:0;right:0;bottom:0;left:0; }
  </style>
</head>

<body>
  <script>
  // Feel free to change or delete any of the code you see in this editor!
    var svg = d3.select("body").append("svg")
      .attr("width", 960)
      .attr("height", 500)
		var svg = d3.select("body").append("svg")
    	.attr("width",960)
    	.attr("height",500);
    
    var flag_data = [{"fill": "blue", "x": 100},
       							 {"fill": "white", "x": 300},
        						 {"fill":"red", "x": 500}];
     	
    console.log(flag_data);
    
    svg.selectAll("rect")
    .data(flag_data)
    //data joint, runs x amount of times without specification
    .enter()
    //specifies functions out side of data()
    .append("rect")
    .attr("y",100)
    .attr("x",function(d) {return d.x;})
    .attr("width",200)
    .attr("height",400)
    .attr("fill", function (d) {return d.fill; });

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