Simple Bar Chart

Creating simple bar chart from a sample data. The chart includes X and Y axes, text on the bars, and mouseover and mouseout functions for hovering over the bars.

<!DOCTYPE html>
<meta charset='utf-8'>
<style> /* CSS styling */

body {
      font-family: 'Helvetica Neue',Helvetica,Arial,sans-serif;
      font-size: 14px;
  }

.bar {
    border: 1px solid #0b3536;
    border-radius: 6px;
    fill: #0098d8;
  }

#viz .barText {
    fill: #f5faf8;
    font-weight: 500;
  }

.axisY text, .axisX text, .headerText text{
    fill: #0b3536;
  }

#viz svg {
    background-color: #f5faf8;
  }

</style>
<head>
  <title>Simple Bar Chart</title>
</head>
<body>
  <div class='container'>
    <div id='viz'></div>
  </div>
<script src='https://d3js.org/d3.v4.min.js'></script>
<script>

// Given sample data
var someData = [ {key: 'W1', value: 32},
                 {key: 'W2', value: 26},
                 {key: 'W3', value: 45},
                 {key: 'W4', value: 38},
                 {key: 'W5', value: 53},
                 {key: 'W6', value: 48},
                 {key: 'W7', value: 42},
                 {key: 'W8', value: 34},
                 {key: 'W9', value: 37},
                 {key: 'W10', value: 36},
];

// Creating new arrays from the data, separating weeks from the numbers
var weeks  = someData.map(function(d){ return d.key; });
var values = someData.map(function(d){ return d.value; });

// Setting the margin and dimensions of the work area
var margin = {top: 50, right: 20, bottom: 30, left: 30},
    width = 760 - margin.left - margin.right,
    height = 380 - margin.top - margin.bottom;

// Creating the scale variables and setting the ranges
var xScale = d3.scaleBand().rangeRound([0, width]).padding(0.1),
    yScale = d3.scaleLinear().rangeRound([height, 0]);

// Adjusting data by assigning domain to the range of the scale
xScale.domain(weeks);
yScale.domain([0, d3.max(values)]);

// Appending the svg object to the div on the page
var svg = d3.select('#viz').append('svg')
    .attr('width', width + margin.left + margin.right)
    .attr('height', height + margin.top + margin.bottom);

// Appending the 'group' element to the svg
// Moving the 'group' element to the top left margin
var g = svg.append('g')
    .attr('transform', 'translate(' + margin.left + ',' + margin.top + ')');

// Adding header to the chart
g.attr('class', 'headerText')
   .append('text')
   .attr('transform', 'translate(' + (width / 2) + ',' + (-margin.top / 2) + ')')
   .attr('text-anchor', 'middle')
   .attr('font-weight', 600)
   .text('Simple Bar Chart');

// Appending X axis and formatting the text
g.append('g')
    .attr('class', 'axisX')
    .attr('transform', 'translate(0,' + height + ')')
    .call(d3.axisBottom(xScale))
    .attr('font-weight', 'bold');

// Appending Y axis
g.append('g')
    .attr('class', 'axisY')
    .call(d3.axisLeft(yScale).ticks(10));

// Creating chart
var chart = g.selectAll('bar')
    .data(someData)
    .enter().append('g')

// Appending bar chart to the chart
chart.append('rect')
    .attr('class', 'bar')
    .attr('x', function(d) { return xScale(d.key); })
    .attr('height', function(d) { return height - yScale(d.value); })
    .attr('y', function(d) { return yScale(d.value); })
    .attr('width', xScale.bandwidth());

// Appending text to each bar chart
chart.append('text')
    .attr('class', 'barText')
    .attr('x', function(d) { return xScale(d.key); })
    .attr('y', function(d) { return yScale(d.value); })
    .attr('dx', xScale.bandwidth()/2)
    .attr('dy', 20)
    .attr('text-anchor', 'middle')
    .text(function(d){ return d.value; });

// Adding mouseover and mouseout functions to the chart
chart.on('mouseover', function(d){
      d3.select(this).attr('opacity', 0.7);
      })
    .on('mouseout', function(d){
      d3.select(this)
        .attr('opacity', 1)});

</script>
</body>

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