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# ASCII Bar Chart
A dynamic, real-time ASCII-based vertical bar chart library that renders beautiful terminal-style visualizations using monospaced characters. Perfect for dashboards, monitoring tools, or any application that needs lightweight, text-based data visualization.
## Features
- 📊 **Real-time Updates**: Add data points dynamically and watch the chart animate
- 📏 **Auto-scaling**: Y-axis automatically adjusts to show min/max values
- 🔤 **Monospaced Rendering**: Uses 'X' characters in Courier font for clean visualization
- 📱 **Responsive**: Automatically adjusts font size to fit container width
- 🏷️ **Customizable Labels**: Add title, X-axis, and vertical Y-axis labels
- 🎯 **Scrolling Data**: Old data automatically scrolls off as new data arrives
- 🎨 **Terminal Theme**: Retro green-on-black aesthetic
## Demo
```
Real-Time Data Visualization
C 20 | X X X X X X X X X X X X X X X X X X X X
o 19 | X X X X X X X X X X X X X X X X X X X X
u 18 | X X X X X X X X X X X X X X X X X X X X
n 17 | X X X X X X X X X X X X X X X X X X X X
t 16 | X X X X X X X X X X X X X X X X X X X X
15 | X X X X X X X X X X X X X X X X X X X X
14 | X X X X X X X X X X X X X X X X X X X X
13 | X X X X X X X X X X X X X X X X X X X X
12 | X X X X X X X X X X X X X X X X X X X X
11 | X X X X X X X X X X X X X X X X X X X X
10 | X X X X X X X X X X X X X X X X X X X X
9 | X X X X X X X X X X X X X X X X X X X X
8 | X X X X X X X X X X X X X X X X X X X X
7 | X X X X X X X X X X X X X X X X X X X X
6 | X X X X X X X X X X X X X X X X X X X X
5 | X X X X X X X X X X X X X X X X X X X X
4 | X X X X X X X X X X X X X X X X X X X X
3 | X X X X X X X X X X X X X X X X X X X X
2 | X X X X X X X X X X X X X X X X X X X X
1 | X X X X X X X X X X X X X X X X X X X X
+----------------------------------------
1 6 11 16 21 26 31 36 41
Time (seconds)
```
## Installation
Simply include the JavaScript file in your HTML:
```html
<script src="ascii-bar-chart.js"></script>
```
## Quick Start
```html
<!DOCTYPE html>
<html>
<head>
<style>
#chart {
font-family: 'Courier New', monospace;
background: #000;
color: #0f0;
padding: 20px;
white-space: pre;
}
</style>
</head>
<body>
<div id="chart"></div>
<script src="ascii-bar-chart.js"></script>
<script>
// Create chart
const chart = new ASCIIBarChart('chart', {
maxHeight: 20,
maxDataPoints: 30,
title: 'My Chart',
xAxisLabel: 'Time',
yAxisLabel: 'Value'
});
// Add data
chart.addValue(15);
chart.addValue(23);
chart.addValue(18);
</script>
</body>
</html>
```
## API Reference
### Constructor
```javascript
new ASCIIBarChart(containerId, options)
```
Creates a new ASCII bar chart instance.
**Parameters:**
| Parameter | Type | Required | Description |
|-----------|------|----------|-------------|
| `containerId` | string | Yes | ID of the HTML element to render the chart in |
| `options` | object | No | Configuration options (see below) |
**Options:**
| Option | Type | Default | Description |
|--------|------|---------|-------------|
| `maxHeight` | number | `20` | Maximum height of the chart in rows |
| `maxDataPoints` | number | `30` | Maximum number of columns before old data scrolls off |
| `title` | string | `''` | Chart title (displayed centered at top) |
| `xAxisLabel` | string | `''` | X-axis label (displayed centered at bottom) |
| `yAxisLabel` | string | `''` | Y-axis label (displayed vertically on left side) |
| `autoFitWidth` | boolean | `true` | Automatically adjust font size to fit container width |
**Example:**
```javascript
const chart = new ASCIIBarChart('my-chart', {
maxHeight: 25,
maxDataPoints: 50,
title: 'Server Response Times',
xAxisLabel: 'Request Number',
yAxisLabel: 'Milliseconds',
autoFitWidth: true
});
```
### Methods
#### `addValue(value)`
Adds a new data point to the chart.
**Parameters:**
- `value` (number): The numeric value to add to the chart
**Example:**
```javascript
chart.addValue(42);
chart.addValue(38);
chart.addValue(45);
```
#### `clear()`
Clears all data from the chart and resets it to initial state.
**Example:**
```javascript
chart.clear();
```
## Features in Detail
### Auto-Scaling Y-Axis
The Y-axis automatically scales to show the full range of your data:
- Minimum value always displays as one 'X' at the bottom
- Maximum value uses the full chart height
- Y-axis labels show actual data values, not just row numbers
- Dynamically adjusts as new data arrives
### Scrolling Data Window
When the number of data points exceeds `maxDataPoints`:
- Old data automatically scrolls off the left side
- X-axis labels update to show actual data point numbers
- Maintains a sliding window of the most recent data
### Responsive Font Sizing
When `autoFitWidth` is enabled:
- Font size automatically adjusts to fill container width
- Responds to window resizing in real-time
- Maintains readability with min/max font size bounds (4px-20px)
- Uses ResizeObserver for efficient updates
### Vertical Y-Axis Label
The Y-axis label is rendered vertically, one character per row:
```
V
a
l
u
e
```
## Advanced Usage
### Real-Time Data Streaming
```javascript
const chart = new ASCIIBarChart('chart', {
maxHeight: 20,
maxDataPoints: 60,
title: 'Live Metrics'
});
// Simulate real-time data
setInterval(() => {
const value = Math.random() * 100;
chart.addValue(value);
}, 1000);
```
### Integration with Data Sources
```javascript
// WebSocket example
const ws = new WebSocket('ws://your-server.com/data');
ws.onmessage = (event) => {
const data = JSON.parse(event.data);
chart.addValue(data.value);
};
// API polling example
async function fetchAndUpdate() {
const response = await fetch('/api/metrics');
const data = await response.json();
chart.addValue(data.currentValue);
}
setInterval(fetchAndUpdate, 5000);
```
### Multiple Charts
```javascript
const cpuChart = new ASCIIBarChart('cpu-chart', {
title: 'CPU Usage %',
yAxisLabel: 'Percent'
});
const memChart = new ASCIIBarChart('mem-chart', {
title: 'Memory Usage MB',
yAxisLabel: 'Megabytes'
});
// Update both charts
cpuChart.addValue(45);
memChart.addValue(2048);
```
## Styling
The chart uses monospaced fonts and renders as plain text. Style the container element:
```css
#chart-container {
font-family: 'Courier New', Courier, monospace;
background-color: #000;
color: #0f0;
padding: 20px;
border: 2px solid #0f0;
border-radius: 5px;
white-space: pre;
overflow-x: auto;
font-size: 12px;
line-height: 1.0;
}
```
## Browser Support
- Modern browsers with ES6 support
- ResizeObserver API (for auto-fit width feature)
- All major browsers: Chrome, Firefox, Safari, Edge
## License
MIT License - feel free to use in your projects!
## Examples
See [`ascii-bar-chart.html`](ascii-bar-chart.html) for a complete working example with:
- Interactive controls (Start/Stop/Reset)
- Configurable settings (update interval, max columns, chart height)
- Test data generator with increasing trend
- Full styling and layout
## Contributing
Contributions welcome! This is a simple, focused library for ASCII-based charting.
## Changelog
### v1.0.0
- Initial release
- Dynamic vertical bar charts
- Auto-scaling Y-axis
- Scrolling data window
- Responsive font sizing
- Customizable labels and titles

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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>ASCII Bar Chart</title>
<style>
body {
background-color: #1e1e1e;
color: #00ff00;
font-family: 'Courier New', Courier, monospace;
padding: 20px;
margin: 0;
}
#chart-container {
background-color: #000;
padding: 20px;
border: 2px solid #00ff00;
border-radius: 5px;
overflow-x: auto;
white-space: pre;
font-size: 8px;
line-height: 1.0;
width: 100%;
box-sizing: border-box;
}
#controls {
margin-bottom: 20px;
}
button {
background-color: #00ff00;
color: #000;
border: none;
padding: 10px 20px;
font-family: 'Courier New', Courier, monospace;
font-size: 14px;
cursor: pointer;
margin-right: 10px;
border-radius: 3px;
}
button:hover {
background-color: #00cc00;
}
#info {
margin-bottom: 10px;
font-size: 12px;
}
#chart-info {
margin-top: 15px;
font-size: 12px;
line-height: 1.6;
}
#chart-info div {
margin-bottom: 5px;
}
#settings {
background-color: #2a2a2a;
padding: 10px;
border-radius: 3px;
border: 1px solid #00ff00;
}
#settings input {
background-color: #1e1e1e;
color: #00ff00;
border: 1px solid #00ff00;
padding: 3px 5px;
font-family: 'Courier New', Courier, monospace;
}
#settings label {
display: inline-block;
}
</style>
</head>
<body>
<h1>ASCII Vertical Bar Chart</h1>
<div id="controls">
<button onclick="dataGenerator.start()">Start</button>
<button onclick="dataGenerator.stop()">Stop</button>
<button onclick="dataGenerator.reset()">Reset</button>
</div>
<div id="settings" style="margin-bottom: 15px; font-size: 12px;">
<label>
Update Interval (ms):
<input type="number" id="update-interval" value="1000" min="100" max="10000" step="100" style="width: 80px;">
</label>
<label style="margin-left: 15px;">
Max Columns:
<input type="number" id="max-columns" value="30" min="10" max="100" step="5" style="width: 60px;">
</label>
<label style="margin-left: 15px;">
Chart Height:
<input type="number" id="chart-height" value="20" min="10" max="50" step="5" style="width: 60px;">
</label>
<button onclick="applySettings()" style="margin-left: 15px; padding: 5px 15px;">Apply Settings</button>
</div>
<div id="info">
<span>Data points: <span id="count">0</span></span> |
<span>Status: <span id="status">Stopped</span></span> |
<span>Next update in: <span id="countdown">--</span>s</span>
</div>
<div id="chart-container"></div>
<div id="chart-info">
<div><strong>Legend:</strong> Each X represents a count unit</div>
<div><strong>Values:</strong> <span id="values">--</span></div>
<div><strong>Max value:</strong> <span id="max-value">--</span>, <strong>Scale:</strong> <span id="scale">--</span></div>
</div>
<!-- Include the ASCII Bar Chart library -->
<script src="ascii-bar-chart.js"></script>
<script>
// Initialize the chart
let chart = new ASCIIBarChart('chart-container', {
maxHeight: 20,
maxDataPoints: 30,
title: 'Real-Time Data Visualization',
xAxisLabel: 'Time (seconds)',
yAxisLabel: 'Count',
autoFitWidth: true // Automatically adjust font size to fit container width
});
// Initial render
chart.render();
chart.updateInfo();
// Test data generator (separate from chart API)
class DataGenerator {
constructor(updateInterval = 1000) {
this.baseValue = 10;
this.intervalId = null;
this.countdownId = null;
this.nextUpdateTime = null;
this.isRunning = false;
this.updateInterval = updateInterval;
}
setUpdateInterval(interval) {
this.updateInterval = interval;
// If running, restart with new interval
if (this.isRunning) {
this.stop();
this.start();
}
}
generateValue() {
// Add some randomness around the base value (±3)
const variation = Math.floor(Math.random() * 7) - 3;
const value = this.baseValue + variation;
// Increase the base value slightly for next time (0.5 to 1.5 increase)
this.baseValue += 0.5 + Math.random();
return Math.max(1, Math.round(value));
}
updateCountdown() {
if (!this.isRunning || !this.nextUpdateTime) {
document.getElementById('countdown').textContent = '--';
return;
}
const now = Date.now();
const remaining = Math.max(0, Math.ceil((this.nextUpdateTime - now) / 1000));
document.getElementById('countdown').textContent = remaining;
}
start() {
if (this.isRunning) return;
this.isRunning = true;
document.getElementById('status').textContent = 'Running';
// Add first data point immediately
chart.addValue(this.generateValue());
// Set up interval for subsequent updates
this.nextUpdateTime = Date.now() + this.updateInterval;
this.intervalId = setInterval(() => {
chart.addValue(this.generateValue());
this.nextUpdateTime = Date.now() + this.updateInterval;
}, this.updateInterval);
// Update countdown every second
this.countdownId = setInterval(() => {
this.updateCountdown();
}, 1000);
this.updateCountdown();
}
stop() {
if (!this.isRunning) return;
this.isRunning = false;
document.getElementById('status').textContent = 'Stopped';
if (this.intervalId) {
clearInterval(this.intervalId);
this.intervalId = null;
}
if (this.countdownId) {
clearInterval(this.countdownId);
this.countdownId = null;
}
this.nextUpdateTime = null;
this.updateCountdown();
}
reset() {
this.stop();
this.baseValue = 10;
chart.clear();
}
}
// Create data generator for testing
let dataGenerator = new DataGenerator(1000);
// Function to apply settings
function applySettings() {
const wasRunning = dataGenerator.isRunning;
// Stop current generator
dataGenerator.stop();
// Get new settings
const updateInterval = parseInt(document.getElementById('update-interval').value);
const maxColumns = parseInt(document.getElementById('max-columns').value);
const chartHeight = parseInt(document.getElementById('chart-height').value);
// Recreate chart with new settings
chart = new ASCIIBarChart('chart-container', {
maxHeight: chartHeight,
maxDataPoints: maxColumns,
title: 'Real-Time Data Visualization',
xAxisLabel: 'Time (seconds)',
yAxisLabel: 'Count',
autoFitWidth: true
});
chart.render();
chart.updateInfo();
// Recreate data generator with new interval
dataGenerator = new DataGenerator(updateInterval);
// Restart if it was running
if (wasRunning) {
dataGenerator.start();
}
}
</script>
</body>
</html>

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/**
* ASCIIBarChart - A dynamic ASCII-based vertical bar chart renderer
*
* Creates real-time animated bar charts using monospaced characters (X)
* with automatic scaling, labels, and responsive font sizing.
*/
class ASCIIBarChart {
/**
* Create a new ASCII bar chart
* @param {string} containerId - The ID of the HTML element to render the chart in
* @param {Object} options - Configuration options
* @param {number} [options.maxHeight=20] - Maximum height of the chart in rows
* @param {number} [options.maxDataPoints=30] - Maximum number of data columns before scrolling
* @param {string} [options.title=''] - Chart title (displayed centered at top)
* @param {string} [options.xAxisLabel=''] - X-axis label (displayed centered at bottom)
* @param {string} [options.yAxisLabel=''] - Y-axis label (displayed vertically on left)
* @param {boolean} [options.autoFitWidth=true] - Automatically adjust font size to fit container width
*/
constructor(containerId, options = {}) {
this.container = document.getElementById(containerId);
this.data = [];
this.maxHeight = options.maxHeight || 20;
this.maxDataPoints = options.maxDataPoints || 30;
this.totalDataPoints = 0; // Track total number of data points added
this.title = options.title || '';
this.xAxisLabel = options.xAxisLabel || '';
this.yAxisLabel = options.yAxisLabel || '';
this.autoFitWidth = options.autoFitWidth !== false; // Default to true
// Set up resize observer if auto-fit is enabled
if (this.autoFitWidth) {
this.resizeObserver = new ResizeObserver(() => {
this.adjustFontSize();
});
this.resizeObserver.observe(this.container);
}
}
/**
* Add a new data point to the chart
* @param {number} value - The numeric value to add
*/
addValue(value) {
this.data.push(value);
this.totalDataPoints++;
// Keep only the most recent data points
if (this.data.length > this.maxDataPoints) {
this.data.shift();
}
this.render();
this.updateInfo();
}
/**
* Clear all data from the chart
*/
clear() {
this.data = [];
this.totalDataPoints = 0;
this.render();
this.updateInfo();
}
/**
* Calculate the width of the chart in characters
* @returns {number} The chart width in characters
* @private
*/
getChartWidth() {
if (this.data.length === 0) return 50; // Default width for empty chart
const yAxisPadding = this.yAxisLabel ? 2 : 0;
const yAxisNumbers = 3; // Width of Y-axis numbers
const separator = 1; // The '|' character
const dataWidth = this.data.length * 2; // Each column is 2 characters wide
const padding = 1; // Extra padding
return yAxisPadding + yAxisNumbers + separator + dataWidth + padding;
}
/**
* Adjust font size to fit container width
* @private
*/
adjustFontSize() {
if (!this.autoFitWidth) return;
const containerWidth = this.container.clientWidth;
const chartWidth = this.getChartWidth();
if (chartWidth === 0) return;
// Calculate optimal font size
// For monospace fonts, character width is approximately 0.6 * font size
const charWidthRatio = 0.6;
const padding = 40; // Account for container padding
const availableWidth = containerWidth - padding;
const optimalFontSize = Math.floor((availableWidth / chartWidth) / charWidthRatio);
// Set reasonable bounds (min 4px, max 20px)
const fontSize = Math.max(4, Math.min(20, optimalFontSize));
this.container.style.fontSize = fontSize + 'px';
this.container.style.lineHeight = '1.0';
}
/**
* Render the chart to the container
* @private
*/
render() {
if (this.data.length === 0) {
this.container.textContent = 'No data yet. Click Start to begin.';
return;
}
let output = '';
const maxValue = Math.max(...this.data);
const minValue = Math.min(...this.data);
const valueRange = maxValue - minValue;
const scale = this.maxHeight;
// Calculate Y-axis label width (for vertical text)
const yLabelWidth = this.yAxisLabel ? 2 : 0;
const yAxisPadding = this.yAxisLabel ? ' ' : '';
// Add title if provided (centered)
if (this.title) {
const chartWidth = 4 + this.data.length * 2; // Y-axis numbers + data columns
const titlePadding = Math.floor((chartWidth - this.title.length) / 2);
output += yAxisPadding + ' '.repeat(Math.max(0, titlePadding)) + this.title + '\n\n';
}
// Draw from top to bottom
for (let row = scale; row > 0; row--) {
let line = '';
// Add vertical Y-axis label character
if (this.yAxisLabel) {
const labelIndex = Math.floor((scale - row) / scale * this.yAxisLabel.length);
if (labelIndex < this.yAxisLabel.length) {
line += this.yAxisLabel[labelIndex] + ' ';
} else {
line += ' ';
}
}
// Calculate the actual value this row represents
const rowValue = minValue + (valueRange * (row - 1) / (scale - 1));
// Add Y-axis label (show actual values)
line += String(Math.round(rowValue)).padStart(3, ' ') + ' |';
// Draw each column
for (let i = 0; i < this.data.length; i++) {
const value = this.data[i];
// Scale the value to fit between 1 and scale
let scaledValue;
if (valueRange === 0) {
// All values are the same
scaledValue = 1;
} else {
scaledValue = 1 + Math.round(((value - minValue) / valueRange) * (scale - 1));
}
if (scaledValue >= row) {
line += ' X';
} else {
line += ' ';
}
}
output += line + '\n';
}
// Draw X-axis
output += yAxisPadding + ' +' + '-'.repeat(this.data.length * 2) + '\n';
// Draw X-axis labels (column numbers that move with the data)
let xAxisLabels = yAxisPadding + ' ';
const startIndex = this.totalDataPoints - this.data.length + 1;
for (let i = 0; i < this.data.length; i++) {
const dataPointNumber = startIndex + i;
if (i % 5 === 0) {
xAxisLabels += String(dataPointNumber).padStart(2, ' ');
} else {
xAxisLabels += ' ';
}
}
output += xAxisLabels + '\n';
// Add X-axis label if provided
if (this.xAxisLabel) {
const labelPadding = Math.floor((this.data.length * 2 - this.xAxisLabel.length) / 2);
output += '\n' + yAxisPadding + ' ' + ' '.repeat(Math.max(0, labelPadding)) + this.xAxisLabel + '\n';
}
this.container.textContent = output;
// Adjust font size to fit width
if (this.autoFitWidth) {
this.adjustFontSize();
}
// Update the external info display
document.getElementById('values').textContent = `[${this.data.join(', ')}]`;
document.getElementById('max-value').textContent = maxValue;
document.getElementById('scale').textContent = `Min: ${minValue}, Max: ${maxValue}, Height: ${scale}`;
}
/**
* Update the info display
* @private
*/
updateInfo() {
document.getElementById('count').textContent = this.data.length;
}
}