Chartjs

Chart.js Skill

Use when building charts and dashboards with Chart.js (v4+).

Key Patterns

Installation

npm install chart.js

Basic Chart

import { Chart, registerables } from 'chart.js';
Chart.register(...registerables);

const ctx = document.getElementById('myChart') as HTMLCanvasElement;
new Chart(ctx, {
  type: 'bar', // 'line' | 'pie' | 'doughnut' | 'radar' | 'scatter' | 'bubble'
  data: {
    labels: ['Jan', 'Feb', 'Mar'],
    datasets: [{
      label: 'Revenue',
      data: [12, 19, 3],
      backgroundColor: 'rgba(54, 162, 235, 0.5)',
      borderColor: 'rgb(54, 162, 235)',
      borderWidth: 1
    }]
  },
  options: {
    responsive: true,
    plugins: { legend: { position: 'top' }, title: { display: true, text: 'Monthly Revenue' } },
    scales: { y: { beginAtZero: true } }
  }
});

React Integration (react-chartjs-2)

import { Bar, Line, Pie } from 'react-chartjs-2';
import { Chart as ChartJS, CategoryScale, LinearScale, BarElement, Title, Tooltip, Legend } from 'chart.js';
ChartJS.register(CategoryScale, LinearScale, BarElement, Title, Tooltip, Legend);

export function Dashboard({ data }) {
  return <Bar data={data} options={{ responsive: true, maintainAspectRatio: false }} />;
}

Real-time Updates

function addData(chart: Chart, label: string, newData: number) {
  chart.data.labels!.push(label);
  chart.data.datasets.forEach((dataset) => dataset.data.push(newData));
  chart.update('none'); // skip animation for perf
}

Dashboard Layout Best Practices

• Use responsive: true and maintainAspectRatio: false for grid layouts
• Register only needed components for smaller bundle: Chart.register(BarElement, CategoryScale, ...)
• Use chart.destroy() before recreating to prevent memory leaks
• For 10k+ data points, use decimation plugin or sample data

Plugin System

const customPlugin = {
  id: 'customBackground',
  beforeDraw: (chart: Chart) => {
    const { ctx, chartArea } = chart;
    ctx.save();
    ctx.fillStyle = '#f0f0f0';
    ctx.fillRect(chartArea.left, chartArea.top, chartArea.width, chartArea.height);
    ctx.restore();
  }
};

Common Pitfalls

• Canvas not found: ensure DOM is ready before creating chart
• Memory leaks: always call chart.destroy() in cleanup/unmount
• Tree-shaking: use named imports from 'chart.js' for smaller bundles
• SSR: Chart.js requires <canvas> — use dynamic import or next/dynamic with ssr: false