rohanreddych/enter-append.html

## enter-append.html
<!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; }
    svg {
      width: 100%;
      height: 100%;
    }
  </style>
</head>

<body>

  <svg>

  </svg>
  <script>
	    var rectWidth = 100;
	    var height = 300;
	    var data = [100, 250, 175, 200, 120];

	    var svg = d3.select('svg');
	    svg.selectAll('rect')
    	.data(data)
    	.enter().append('rect')
    	.attr('x', (d, i) => i * rectWidth)
    	.attr('y', d => height - d)
    	.attr('width', rectWidth)
    	.attr('height', d => d)
    	.attr('fill', function(d){
	    	if (d === 250){
		    	return "red";
		    }
		    else{
			    return "blue";
			}
    	})
    	.attr('stroke', '#fff');

  </script>
</body>

## simple-d3.html
<!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; }
    svg {
      width: 100%;
      height: 100%;
    }
  </style>
</head>

<body>

  <svg>
    <rect />
    <rect />
    <rect />
    <rect />
    <rect />
  </svg>
  <script>
	var rectWidth = 100;
    var height = 300;
    var data = [100, 250, 175, 200, 120];

    var rect = d3.selectAll('rect')
    	.data(data)
    	.attr('x', function(d, i) {return i * rectWidth})
    	.attr('y', function(d) {return height - d})
    	.attr('width', rectWidth)
    	.attr('height', function(d) {return d})
    	.attr('fill', 'blue')
    	.attr('stroke', '#fff');
  </script>
</body>

## transition.html
<!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; }
    svg {
      width: 100%;
      height: 100%;
    }
  </style>
</head>

<body>
  <svg></svg>
  <script>
		var rectWidth = 100;
    var height = 300;
    var data = [
      [100, 250, 175, 200, 120],
      [230, 120, 300, 145, 75, 250],
      [240, 250, 100]
    ];


    var colors = d3.scaleOrdinal(d3.schemeCategory10);
    var svg = d3.select('svg');

    function updateBars(data) {
      var t = d3.transition().duration(2000);

      var bars = svg.selectAll('rect')
        .data(data, d => d);

      // exit
      bars.exit().transition(t)
				.attr('y', height)
        .attr('height', 0)
        .remove();

      // enter
      var enter = bars.enter().append('rect')
        .attr('width', rectWidth)
        .attr('stroke', '#fff')
      	.attr('y', height)
        .attr('x', (d, i) => i * rectWidth);
      // enter + update
      bars = enter.merge(bars)
        .attr('fill', d => colors(d))
      	.transition(t)
        .attr('x', (d, i) => i * rectWidth)
        .attr('y', d => height - d)
        .attr('height', d => d);
    }

    var index = 0;
    setInterval(() => {
      updateBars(data[index % 3]);
      index += 1;
    }, 2000);
  </script>
</body>
	<!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; }
	svg {
	width: 100%;
	height: 100%;
	}
	</style>
	</head>

	<body>

	<svg>

	</svg>
	<script>
	var rectWidth = 100;
	var height = 300;
	var data = [100, 250, 175, 200, 120];

	var svg = d3.select('svg');
	svg.selectAll('rect')
	.data(data)
	.enter().append('rect')
	.attr('x', (d, i) => i * rectWidth)
	.attr('y', d => height - d)
	.attr('width', rectWidth)
	.attr('height', d => d)
	.attr('fill', function(d){
	if (d === 250){
	return "red";
	}
	else{
	return "blue";
	}
	})
	.attr('stroke', '#fff');

	</script>
	</body>