making gene rectangles

<!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>
    // copy the .json data into a new blockbuilder tab. strings should be in double quotes
    //read in the data with d3.json.("filename", function(erro,ANYNAME))
    //check this by console.log(ANYNAME)
  d3.json("data.json", function(error, json)  {
		//make an svg with those attirbutes
    var svg = d3.select("body").append("svg")	
  	.attr("width", 1000)
  	.attr("height", 1000)
    //Select the svg and put some rectuangles in it
  d3.select("svg").selectAll("rect")
   		//use the .data function to tell it where to get the data from
    	.data(json)
  		//enter data from the data.json file into the DOM. Remember d3 is the glue between the data and the DOM (document object model)
   		.enter() //there's stuff in the data that's not in the DOM and it needs to be entered.
   		.append("rect") //modify the rectangles. 
  			.attr("y", 50) //we want all the genes in the same y value so we set that.
      	.attr("height", 50) //this is the same for every gene
    		.attr("x", function(d) {return d.start - d.start}) //width depends on data. the d is a convension that everyone uses and statys the same. For each gene called d return the start
  	  	.attr("width", function(d) {return d.stop - d.start}) //the larger number - smaller number
  		//set the color based on the data	
    	.attr("fill", function(d) {if (d.orientation == "foward")
              {return "green" ;}
  						else if(d.orientation == "reverse")
                {return "red"}
   	});
  })
  </script>
</body>

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