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Introduction to plotly.js — an open source graphing library

Plotly.js is a library suited for JavaScript applications which make use of graphs and charts. There are a few reasons to consider using it for your next project:

  1. Plotly.js uses both D3.js and stack.gl
  2. Plotly.js ships with 20 chart types, including 3D charts, statistical graphs, and SVG maps
  3. It is an open source library

It has more than 9900 stars on Github

There are 2 main concepts in Plotly :

1. Data
2. Layout

Data

The Data object defines what we want to display in the chart (that is, the data). We define a collection of data and the specifications to display them as a trace. A Data object can have many traces. Think of a line chart with two lines representing two different categories: each line is a trace.

Layout

The Layout object defines features that are not related to data (like title, axis titles, and so on). We can also use the Layout to add annotations and shapes to the chart.

Let’s looks at the setup :

First, include the file from CDN

<head>
  <!-- Plotly.js -->
  <script src="https://cdn.plot.ly/plotly-latest.min.js"></script>
</head>

Next, let’s plot a line graph :

HTML :

<head>
  <!-- Plotly.js -->
  <script src="https://cdn.plot.ly/plotly-latest.min.js"></script>
</head>

<body>
  
  <div id="myDiv">
	<!-- Plotly chart will be drawn inside this DIV -->
  </div>

</body>

JS :

var trace1 = {
  x: [11, 12, 13, 14],
  y: [19, 14, 12, 16],
  type: 'scatter',
};

var trace2 = {
  x: [12, 22, 23, 24],
  y: [15, 4, 10, 8],
  type: 'scatter'
};

var data = [trace1, trace2];

Plotly.newPlot('myDiv', data);

Result :

Basic setup can be done with a file inclusion, a DOM element, and a script for plotting.
After the inclusion of the Plotly.js library in , we have defined an empty <div> to plot the graph.
Plotly.new() draws a new plot in the element.
We can have a Line and Scatter Plot charts by inclusion of mode in the trace variable.
The legend in a graph is linked to the data being graphically displayed in the plot area of the chart.
We can customize charts by using different options like legend name, marker color, marker size, line color, line width, chart title, mode, etc.

Example :

HTML :

<head>
  <!-- Plotly.js -->
  <script src="https://cdn.plot.ly/plotly-latest.min.js"></script>
</head>

<body>
  
  <div id="myDiv">
	<!-- Plotly chart will be drawn inside this DIV -->
  </div>
  
  <script>
    <!-- JAVASCRIPT CODE GOES HERE -->
  </script>

</body>

JS :

var trace1 = {
  x: [11, 12, 13, 14],
  y: [11, 14, 12, 16],
  mode: 'markers',
  name : "Apple",
  marker: {
    color: 'rgb(219, 64, 82)',
    size: 13
  }
};

var trace2 = {
  x: [12, 13, 14, 15],
  y: [17, 15, 10, 19],
  mode: 'lines',
  name : "Mangoes",
  line: {
    color: 'rgb(55, 128, 191)',
    width: 6
  }
};

var trace3 = {
  x: [11, 21, 31, 41],
  y: [14, 19, 16, 13],
  mode: 'lines+markers',
  name : "grapes",
  marker: {
    color: 'rgb(128, 0, 128)',
    size: 9
  },
  line: {
    color: 'rgb(128, 0, 128)',
    width: 2
  }
};

var data = [trace1, trace2, trace3];

var layout = {
  title: 'Line and Scatter Styling Example'
};

Plotly.newPlot('myDiv', data, layout);

Result :

If we use markers as we have used in trace1 , notice that we only get points marked in the graph coordinates and do not see the connected line across all points

By now we have seen some examples of line, let’s quickly plot a bar chart using ‘bar’ as type.

Example :

HTML :

<head>
  <!-- Plotly.js -->
  <script src="https://cdn.plot.ly/plotly-latest.min.js"></script>
</head>

<body>
  
  <div id="myDiv"><!-- Plotly chart will be drawn inside this DIV --></div>
  <script>
    <!-- JAVASCRIPT CODE GOES HERE -->
  </script>
</body>

JS :

var data = [{
  x: ['lions', 'tigers','monkeys'],
  y: [21, 15, 24],
  type: 'bar'
}];

Plotly.newPlot('myDiv', data);

Result :

Did you found this article helpful ? I try my best to write a deep dive article.

I had a pretty good experience with Plotly. What are your thoughts about it after this overview ? And what other tools do you use to generate charts for the web ? Share them in the comments!

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