Build an HTML5 Spreadsheet-Like Graph Plotter with JavaScript

Have you ever wanted to create a simple graphing tool using just HTML5 and JavaScript? In this tutorial, I’ll show you how to build a spreadsheet-style data input table that plots dynamic bar and line graphs using the <canvas> element — no external libraries required.

This project is perfect for JavaScript beginners, especially if you enjoy learning through hands-on examples.

🎯 What You’ll Learn

How to use <input type="number"> in a spreadsheet-style table
Automatically add new rows when inputs are filled
Draw bar and line graphs using the HTML5 <canvas>
Add interactivity with JavaScript
Toggle between graph types using a dropdown

📑 Project Code Overview

We’ll create:

A simple table with two columns for X and Y values
Auto-expanding rows when both X and Y are filled
A dropdown to choose between Line or Bar graph
Canvas rendering logic to draw and update the graph

💻 Technologies Used

HTML5 for structure and canvas
CSS3 for minimal styling
Vanilla JavaScript for dynamic interaction

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8" />
  <title>Line/Bar Graph Plotter</title>
  <style>
    body {
      font-family: sans-serif;
      padding: 20px;
      background: #f0f0f0;
    }

    table {
      width: 300px;
      margin-bottom: 10px;
      border-collapse: collapse;
    }

    th, td {
      padding: 6px;
      border: 1px solid #ccc;
      text-align: center;
    }

    input[type="number"] {
      width: 80px;
      padding: 4px;
      text-align: right;
    }

    select, button {
      padding: 8px 12px;
      margin: 10px 0;
      font-size: 14px;
    }

    canvas {
      border: 1px solid #333;
      background: #fff;
      display: block;
      margin-top: 20px;
    }
  </style>
</head>
<body>

  <h2>Spreadsheet Graph Plotter</h2>

  <label>Choose Graph Type:</label>
  <select id="graphType">
    <option value="line">Line Graph</option>
    <option value="bar">Bar Graph</option>
  </select>

  <table id="dataTable">
    <thead>
      <tr><th>X</th><th>Y</th></tr>
    </thead>
    <tbody>
      <tr>
        <td><input type="number" step="any" /></td>
        <td><input type="number" step="any" /></td>
      </tr>
    </tbody>
  </table>

  <button onclick="plotGraph()">Plot Graph</button>

  <canvas id="graphCanvas" width="600" height="400"></canvas>

  <script>
    const table = document.getElementById('dataTable').getElementsByTagName('tbody')[0];

    // Add new row if last one is filled
    table.addEventListener('input', () => {
      const rows = table.rows;
      const lastRow = rows[rows.length - 1];
      const xInput = lastRow.cells[0].querySelector('input');
      const yInput = lastRow.cells[1].querySelector('input');

      if (xInput.value && yInput.value) {
        addRow();
      }
    });

    function addRow() {
      const newRow = table.insertRow();
      const xCell = newRow.insertCell(0);
      const yCell = newRow.insertCell(1);

      const xInput = document.createElement('input');
      xInput.type = 'number';
      xInput.step = 'any';

      const yInput = document.createElement('input');
      yInput.type = 'number';
      yInput.step = 'any';

      xCell.appendChild(xInput);
      yCell.appendChild(yInput);
    }

function plotGraph() {
  const graphType = document.getElementById("graphType").value;
  const canvas = document.getElementById("graphCanvas");
  const ctx = canvas.getContext("2d");
  ctx.clearRect(0, 0, canvas.width, canvas.height);

  let points = [];

  const rows = table.rows;
  for (let i = 0; i < rows.length; i++) {
    const x = parseFloat(rows[i].cells[0].querySelector('input').value);
    const y = parseFloat(rows[i].cells[1].querySelector('input').value);
    if (!isNaN(x) && !isNaN(y)) {
      points.push({ x, y });
    }
  }

  if (points.length < 2) {
    alert("Please enter at least two valid data points.");
    return;
  }

  if (graphType === 'line') {
    points.sort((a, b) => a.x - b.x);
  }

  const padding = 40;
  const graphWidth = canvas.width - 2 * padding;
  const graphHeight = canvas.height - 2 * padding;
  const xVals = points.map(p => p.x);
  const yVals = points.map(p => p.y);

  const xMin = Math.min(...xVals);
  const xMax = Math.max(...xVals);
  const yMin = Math.min(0, ...yVals);
  const yMax = Math.max(...yVals);

  const xScale = graphWidth / (xMax - xMin || 1);
  const yScale = graphHeight / (yMax - yMin || 1);

  // Axes
  ctx.strokeStyle = "#999";
  ctx.lineWidth = 1;
  ctx.beginPath();
  ctx.moveTo(padding, canvas.height - padding);
  ctx.lineTo(canvas.width - padding, canvas.height - padding); // X-axis
  ctx.moveTo(padding, padding);
  ctx.lineTo(padding, canvas.height - padding); // Y-axis
  ctx.stroke();

  if (graphType === 'line') {
    // ✅ Draw a single path through all sorted points
    ctx.strokeStyle = "#007acc";
    ctx.lineWidth = 2;
    ctx.beginPath();

    points.forEach((point, i) => {
      const xCoord = padding + (point.x - xMin) * xScale;
      const yCoord = canvas.height - padding - (point.y - yMin) * yScale;

      if (i === 0) {
        ctx.moveTo(xCoord, yCoord);
      } else {
        ctx.lineTo(xCoord, yCoord);
      }
    });

    ctx.stroke(); // ⬅️ Only stroke once, after path is fully defined

    // ✅ Draw data points on top
    points.forEach(point => {
      const xCoord = padding + (point.x - xMin) * xScale;
      const yCoord = canvas.height - padding - (point.y - yMin) * yScale;
      ctx.fillStyle = "#ff3333";
      ctx.beginPath();
      ctx.arc(xCoord, yCoord, 4, 0, 2 * Math.PI);
      ctx.fill();
    });
  }

  if (graphType === 'bar') {
    // Draw bars centered on each x
    const barWidth = Math.min(40, graphWidth / xVals.length - 10);

    points.forEach((point) => {
      const xCoord = padding + (point.x - xMin) * xScale - barWidth / 2;
      const yCoord = canvas.height - padding - (point.y - yMin) * yScale;
      const barHeight = (point.y - yMin) * yScale;

      ctx.fillStyle = "#28a745";
      ctx.fillRect(xCoord, yCoord, barWidth, barHeight);
    });
  }
}

</script>

</body>
</html>

Interactive Demo

Here’s a live example of the Spreadsheet Graph in action:

HTML5 Spreadsheet Graph Demo

Web Browser Displaying HTML5 Spreadsheet Line Graph

Web Browser Displaying HTML5 Spreadsheet Bar Graph

HTML5 Spreadsheet Graph Video

📚 Want to Learn JavaScript More Deeply?

Check out my beginner-friendly book:
📖 Learning JavaScript – A Beginner’s Guide

Whether you’re starting fresh or revisiting JavaScript, this book is a solid companion.

Also, explore my full course here:
🎓 Learning JavaScript – Online Course

👨‍🎓 Need Help or 1-on-1 Tutoring?

I’m available for personalized programming tutorials — including HTML5, CSS, JavaScript, and more.
📧 Contact me here to book a session.

🔁 What’s Next?

In future tutorials, I’ll cover:

Adding axis labels and gridlines
Exporting graphs as images
Saving input data to local storage or files

💬 Questions?

Have any questions or feedback? Leave a comment below or reach out through the contact form.

Happy coding!

Recommended Resources:

Disclosure: Some of the links above are referral (affiliate) links. I may earn a commission if you purchase through them - at no extra cost to you.