D3.js Visualisation Overview

This skill provides guidance for creating sophisticated, interactive data visualisations using d3.js. D3.js (Data-Driven Documents) excels at binding data to DOM elements and applying data-driven transformations to create custom, publication-quality visualisations with precise control over every visual element. The techniques work across any JavaScript environment, including vanilla JavaScript, React, Vue, Svelte, and other frameworks.

When to use d3.js

Use d3.js for:

Custom visualisations requiring unique visual encodings or layouts Interactive explorations with complex pan, zoom, or brush behaviours Network/graph visualisations (force-directed layouts, tree diagrams, hierarchies, chord diagrams) Geographic visualisations with custom projections Visualisations requiring smooth, choreographed transitions Publication-quality graphics with fine-grained styling control Novel chart types not available in standard libraries

Consider alternatives for:

3D visualisations - use Three.js instead Core workflow 1. Set up d3.js

Import d3 at the top of your script:

import * as d3 from 'd3';

Or use the CDN version (7.x):

All modules (scales, axes, shapes, transitions, etc.) are accessible through the d3 namespace.

Choose the integration pattern

Pattern A: Direct DOM manipulation (recommended for most cases) Use d3 to select DOM elements and manipulate them imperatively. This works in any JavaScript environment:

function drawChart(data) { if (!data || data.length === 0) return;

const svg = d3.select('#chart'); // Select by ID, class, or DOM element

// Clear previous content svg.selectAll("*").remove();

// Set up dimensions const width = 800; const height = 400; const margin = { top: 20, right: 30, bottom: 40, left: 50 };

// Create scales, axes, and draw visualisation // ... d3 code here ... }

// Call when data changes drawChart(myData);

Pattern B: Declarative rendering (for frameworks with templating) Use d3 for data calculations (scales, layouts) but render elements via your framework:

function getChartElements(data) { const xScale = d3.scaleLinear() .domain([0, d3.max(data, d => d.value)]) .range([0, 400]);

return data.map((d, i) => ({ x: 50, y: i * 30, width: xScale(d.value), height: 25 })); }

// In React: {getChartElements(data).map((d, i) => )} // In Vue: v-for directive over the returned array // In vanilla JS: Create elements manually from the returned data

Use Pattern A for complex visualisations with transitions, interactions, or when leveraging d3's full capabilities. Use Pattern B for simpler visualisations or when your framework prefers declarative rendering.

Structure the visualisation code

Follow this standard structure in your drawing function:

function drawVisualization(data) { if (!data || data.length === 0) return;

const svg = d3.select('#chart'); // Or pass a selector/element svg.selectAll("*").remove(); // Clear previous render

// 1. Define dimensions const width = 800; const height = 400; const margin = { top: 20, right: 30, bottom: 40, left: 50 }; const innerWidth = width - margin.left - margin.right; const innerHeight = height - margin.top - margin.bottom;

// 2. Create main group with margins const g = svg.append("g") .attr("transform", translate(${margin.left},${margin.top}));

// 3. Create scales const xScale = d3.scaleLinear() .domain([0, d3.max(data, d => d.x)]) .range([0, innerWidth]);

const yScale = d3.scaleLinear() .domain([0, d3.max(data, d => d.y)]) .range([innerHeight, 0]); // Note: inverted for SVG coordinates

// 4. Create and append axes const xAxis = d3.axisBottom(xScale); const yAxis = d3.axisLeft(yScale);

g.append("g") .attr("transform", translate(0,${innerHeight})) .call(xAxis);

g.append("g") .call(yAxis);

// 5. Bind data and create visual elements g.selectAll("circle") .data(data) .join("circle") .attr("cx", d => xScale(d.x)) .attr("cy", d => yScale(d.y)) .attr("r", 5) .attr("fill", "steelblue"); }

// Call when data changes drawVisualization(myData);

Implement responsive sizing

Make visualisations responsive to container size:

function setupResponsiveChart(containerId, data) { const container = document.getElementById(containerId); const svg = d3.select(#${containerId}).append('svg');

function updateChart() { const { width, height } = container.getBoundingClientRect(); svg.attr('width', width).attr('height', height);

// Redraw visualisation with new dimensions
drawChart(data, svg, width, height);

}

// Update on initial load updateChart();

// Update on window resize window.addEventListener('resize', updateChart);

// Return cleanup function return () => window.removeEventListener('resize', updateChart); }

// Usage: // const cleanup = setupResponsiveChart('chart-container', myData); // cleanup(); // Call when component unmounts or element removed

Or use ResizeObserver for more direct container monitoring:

function setupResponsiveChartWithObserver(svgElement, data) { const observer = new ResizeObserver(() => { const { width, height } = svgElement.getBoundingClientRect(); d3.select(svgElement) .attr('width', width) .attr('height', height);

// Redraw visualisation
drawChart(data, d3.select(svgElement), width, height);

});

observer.observe(svgElement.parentElement); return () => observer.disconnect(); }

Common visualisation patterns Bar chart function drawBarChart(data, svgElement) { if (!data || data.length === 0) return;

const svg = d3.select(svgElement); svg.selectAll("*").remove();

const width = 800; const height = 400; const margin = { top: 20, right: 30, bottom: 40, left: 50 }; const innerWidth = width - margin.left - margin.right; const innerHeight = height - margin.top - margin.bottom;

const g = svg.append("g") .attr("transform", translate(${margin.left},${margin.top}));

const xScale = d3.scaleBand() .domain(data.map(d => d.category)) .range([0, innerWidth]) .padding(0.1);

const yScale = d3.scaleLinear() .domain([0, d3.max(data, d => d.value)]) .range([innerHeight, 0]);

g.append("g") .attr("transform", translate(0,${innerHeight})) .call(d3.axisBottom(xScale));

g.append("g") .call(d3.axisLeft(yScale));

g.selectAll("rect") .data(data) .join("rect") .attr("x", d => xScale(d.category)) .attr("y", d => yScale(d.value)) .attr("width", xScale.bandwidth()) .attr("height", d => innerHeight - yScale(d.value)) .attr("fill", "steelblue"); }

// Usage: // drawBarChart(myData, document.getElementById('chart'));

Line chart const line = d3.line() .x(d => xScale(d.date)) .y(d => yScale(d.value)) .curve(d3.curveMonotoneX); // Smooth curve

g.append("path") .datum(data) .attr("fill", "none") .attr("stroke", "steelblue") .attr("stroke-width", 2) .attr("d", line);

Scatter plot g.selectAll("circle") .data(data) .join("circle") .attr("cx", d => xScale(d.x)) .attr("cy", d => yScale(d.y)) .attr("r", d => sizeScale(d.size)) // Optional: size encoding .attr("fill", d => colourScale(d.category)) // Optional: colour encoding .attr("opacity", 0.7);

Chord diagram

A chord diagram shows relationships between entities in a circular layout, with ribbons representing flows between them:

function drawChordDiagram(data) { // data format: array of objects with source, target, and value // Example: [{ source: 'A', target: 'B', value: 10 }, ...]

if (!data || data.length === 0) return;

const svg = d3.select('#chart'); svg.selectAll("*").remove();

const width = 600; const height = 600; const innerRadius = Math.min(width, height) * 0.3; const outerRadius = innerRadius + 30;

// Create matrix from data const nodes = Array.from(new Set(data.flatMap(d => [d.source, d.target]))); const matrix = Array.from({ length: nodes.length }, () => Array(nodes.length).fill(0));

data.forEach(d => { const i = nodes.indexOf(d.source); const j = nodes.indexOf(d.target); matrix[i][j] += d.value; matrix[j][i] += d.value; });

// Create chord layout const chord = d3.chord() .padAngle(0.05) .sortSubgroups(d3.descending);

const arc = d3.arc() .innerRadius(innerRadius) .outerRadius(outerRadius);

const ribbon = d3.ribbon() .source(d => d.source) .target(d => d.target);

const colourScale = d3.scaleOrdinal(d3.schemeCategory10) .domain(nodes);

const g = svg.append("g") .attr("transform", translate(${width / 2},${height / 2}));

const chords = chord(matrix);

// Draw ribbons g.append("g") .attr("fill-opacity", 0.67) .selectAll("path") .data(chords) .join("path") .attr("d", ribbon) .attr("fill", d => colourScale(nodes[d.source.index])) .attr("stroke", d => d3.rgb(colourScale(nodes[d.source.index])).darker());

// Draw groups (arcs) const group = g.append("g") .selectAll("g") .data(chords.groups) .join("g");

group.append("path") .attr("d", arc) .attr("fill", d => colourScale(nodes[d.index])) .attr("stroke", d => d3.rgb(colourScale(nodes[d.index])).darker());

// Add labels group.append("text") .each(d => { d.angle = (d.startAngle + d.endAngle) / 2; }) .attr("dy", "0.31em") .attr("transform", d => rotate(${(d.angle * 180 / Math.PI) - 90})translate(${outerRadius + 30})${d.angle > Math.PI ? "rotate(180)" : ""}) .attr("text-anchor", d => d.angle > Math.PI ? "end" : null) .text((d, i) => nodes[i]) .style("font-size", "12px"); }

Heatmap

A heatmap uses colour to encode values in a two-dimensional grid, useful for showing patterns across categories:

function drawHeatmap(data) { // data format: array of objects with row, column, and value // Example: [{ row: 'A', column: 'X', value: 10 }, ...]

if (!data || data.length === 0) return;

const svg = d3.select('#chart'); svg.selectAll("*").remove();

const width = 800; const height = 600; const margin = { top: 100, right: 30, bottom: 30, left: 100 }; const innerWidth = width - margin.left - margin.right; const innerHeight = height - margin.top - margin.bottom;

// Get unique rows and columns const rows = Array.from(new Set(data.map(d => d.row))); const columns = Array.from(new Set(data.map(d => d.column)));

const g = svg.append("g") .attr("transform", translate(${margin.left},${margin.top}));

// Create scales const xScale = d3.scaleBand() .domain(columns) .range([0, innerWidth]) .padding(0.01);

const yScale = d3.scaleBand() .domain(rows) .range([0, innerHeight]) .padding(0.01);

// Colour scale for values const colourScale = d3.scaleSequential(d3.interpolateYlOrRd) .domain([0, d3.max(data, d => d.value)]);

// Draw rectangles g.selectAll("rect") .data(data) .join("rect") .attr("x", d => xScale(d.column)) .attr("y", d => yScale(d.row)) .attr("width", xScale.bandwidth()) .attr("height", yScale.bandwidth()) .attr("fill", d => colourScale(d.value));

// Add x-axis labels svg.append("g") .attr("transform", translate(${margin.left},${margin.top})) .selectAll("text") .data(columns) .join("text") .attr("x", d => xScale(d) + xScale.bandwidth() / 2) .attr("y", -10) .attr("text-anchor", "middle") .text(d => d) .style("font-size", "12px");

// Add y-axis labels svg.append("g") .attr("transform", translate(${margin.left},${margin.top})) .selectAll("text") .data(rows) .join("text") .attr("x", -10) .attr("y", d => yScale(d) + yScale.bandwidth() / 2) .attr("dy", "0.35em") .attr("text-anchor", "end") .text(d => d) .style("font-size", "12px");

// Add colour legend const legendWidth = 20; const legendHeight = 200; const legend = svg.append("g") .attr("transform", translate(${width - 60},${margin.top}));

const legendScale = d3.scaleLinear() .domain(colourScale.domain()) .range([legendHeight, 0]);

const legendAxis = d3.axisRight(legendScale) .ticks(5);

// Draw colour gradient in legend for (let i = 0; i < legendHeight; i++) { legend.append("rect") .attr("y", i) .attr("width", legendWidth) .attr("height", 1) .attr("fill", colourScale(legendScale.invert(i))); }

legend.append("g") .attr("transform", translate(${legendWidth},0)) .call(legendAxis); }

Pie chart const pie = d3.pie() .value(d => d.value) .sort(null);

const arc = d3.arc() .innerRadius(0) .outerRadius(Math.min(width, height) / 2 - 20);

const colourScale = d3.scaleOrdinal(d3.schemeCategory10);

const g = svg.append("g") .attr("transform", translate(${width / 2},${height / 2}));

g.selectAll("path") .data(pie(data)) .join("path") .attr("d", arc) .attr("fill", (d, i) => colourScale(i)) .attr("stroke", "white") .attr("stroke-width", 2);

Force-directed network const simulation = d3.forceSimulation(nodes) .force("link", d3.forceLink(links).id(d => d.id).distance(100)) .force("charge", d3.forceManyBody().strength(-300)) .force("center", d3.forceCenter(width / 2, height / 2));

const link = g.selectAll("line") .data(links) .join("line") .attr("stroke", "#999") .attr("stroke-width", 1);

const node = g.selectAll("circle") .data(nodes) .join("circle") .attr("r", 8) .attr("fill", "steelblue") .call(d3.drag() .on("start", dragstarted) .on("drag", dragged) .on("end", dragended));

simulation.on("tick", () => { link .attr("x1", d => d.source.x) .attr("y1", d => d.source.y) .attr("x2", d => d.target.x) .attr("y2", d => d.target.y);

node .attr("cx", d => d.x) .attr("cy", d => d.y); });

function dragstarted(event) { if (!event.active) simulation.alphaTarget(0.3).restart(); event.subject.fx = event.subject.x; event.subject.fy = event.subject.y; }

function dragged(event) { event.subject.fx = event.x; event.subject.fy = event.y; }

function dragended(event) { if (!event.active) simulation.alphaTarget(0); event.subject.fx = null; event.subject.fy = null; }

Adding interactivity Tooltips // Create tooltip div (outside SVG) const tooltip = d3.select("body").append("div") .attr("class", "tooltip") .style("position", "absolute") .style("visibility", "hidden") .style("background-color", "white") .style("border", "1px solid #ddd") .style("padding", "10px") .style("border-radius", "4px") .style("pointer-events", "none");

// Add to elements circles .on("mouseover", function(event, d) { d3.select(this).attr("opacity", 1); tooltip .style("visibility", "visible") .html(<strong>${d.label}</strong><br/>Value: ${d.value}); }) .on("mousemove", function(event) { tooltip .style("top", (event.pageY - 10) + "px") .style("left", (event.pageX + 10) + "px"); }) .on("mouseout", function() { d3.select(this).attr("opacity", 0.7); tooltip.style("visibility", "hidden"); });

Zoom and pan const zoom = d3.zoom() .scaleExtent([0.5, 10]) .on("zoom", (event) => { g.attr("transform", event.transform); });

svg.call(zoom);

Click interactions circles .on("click", function(event, d) { // Handle click (dispatch event, update app state, etc.) console.log("Clicked:", d);

// Visual feedback
d3.selectAll("circle").attr("fill", "steelblue");
d3.select(this).attr("fill", "orange");

// Optional: dispatch custom event for your framework/app to listen to
// window.dispatchEvent(new CustomEvent('chartClick', { detail: d }));

});

Transitions and animations

Add smooth transitions to visual changes:

// Basic transition circles .transition() .duration(750) .attr("r", 10);

// Chained transitions circles .transition() .duration(500) .attr("fill", "orange") .transition() .duration(500) .attr("r", 15);

// Staggered transitions circles .transition() .delay((d, i) => i * 50) .duration(500) .attr("cy", d => yScale(d.value));

// Custom easing circles .transition() .duration(1000) .ease(d3.easeBounceOut) .attr("r", 10);

Scales reference Quantitative scales // Linear scale const xScale = d3.scaleLinear() .domain([0, 100]) .range([0, 500]);

// Log scale (for exponential data) const logScale = d3.scaleLog() .domain([1, 1000]) .range([0, 500]);

// Power scale const powScale = d3.scalePow() .exponent(2) .domain([0, 100]) .range([0, 500]);

// Time scale const timeScale = d3.scaleTime() .domain([new Date(2020, 0, 1), new Date(2024, 0, 1)]) .range([0, 500]);

Ordinal scales // Band scale (for bar charts) const bandScale = d3.scaleBand() .domain(['A', 'B', 'C', 'D']) .range([0, 400]) .padding(0.1);

// Point scale (for line/scatter categories) const pointScale = d3.scalePoint() .domain(['A', 'B', 'C', 'D']) .range([0, 400]);

// Ordinal scale (for colours) const colourScale = d3.scaleOrdinal(d3.schemeCategory10);

Sequential scales // Sequential colour scale const colourScale = d3.scaleSequential(d3.interpolateBlues) .domain([0, 100]);

// Diverging colour scale const divScale = d3.scaleDiverging(d3.interpolateRdBu) .domain([-10, 0, 10]);

Best practices Data preparation

Always validate and prepare data before visualisation:

// Filter invalid values const cleanData = data.filter(d => d.value != null && !isNaN(d.value));

// Sort data if order matters const sortedData = [...data].sort((a, b) => b.value - a.value);

// Parse dates const parsedData = data.map(d => ({ ...d, date: d3.timeParse("%Y-%m-%d")(d.date) }));

Performance optimisation

For large datasets (>1000 elements):

// Use canvas instead of SVG for many elements // Use quadtree for collision detection // Simplify paths with d3.line().curve(d3.curveStep) // Implement virtual scrolling for large lists // Use requestAnimationFrame for custom animations

Accessibility

Make visualisations accessible:

// Add ARIA labels svg.attr("role", "img") .attr("aria-label", "Bar chart showing quarterly revenue");

// Add title and description svg.append("title").text("Quarterly Revenue 2024"); svg.append("desc").text("Bar chart showing revenue growth across four quarters");

// Ensure sufficient colour contrast // Provide keyboard navigation for interactive elements // Include data table alternative

Styling

Use consistent, professional styling:

// Define colour palettes upfront const colours = { primary: '#4A90E2', secondary: '#7B68EE', background: '#F5F7FA', text: '#333333', gridLines: '#E0E0E0' };

// Apply consistent typography svg.selectAll("text") .style("font-family", "Inter, sans-serif") .style("font-size", "12px");

// Use subtle grid lines g.selectAll(".tick line") .attr("stroke", colours.gridLines) .attr("stroke-dasharray", "2,2");

Common issues and solutions

Issue: Axes not appearing

Ensure scales have valid domains (check for NaN values) Verify axis is appended to correct group Check transform translations are correct

Issue: Transitions not working

Call .transition() before attribute changes Ensure elements have unique keys for proper data binding Check that useEffect dependencies include all changing data

Issue: Responsive sizing not working

Use ResizeObserver or window resize listener Update dimensions in state to trigger re-render Ensure SVG has width/height attributes or viewBox

Issue: Performance problems

Limit number of DOM elements (consider canvas for >1000 items) Debounce resize handlers Use .join() instead of separate enter/update/exit selections Avoid unnecessary re-renders by checking dependencies Resources references/

Contains detailed reference materials:

d3-patterns.md - Comprehensive collection of visualisation patterns and code examples scale-reference.md - Complete guide to d3 scales with examples colour-schemes.md - D3 colour schemes and palette recommendations assets/

Contains boilerplate templates:

chart-template.js - Starter template for basic chart interactive-template.js - Template with tooltips, zoom, and interactions sample-data.json - Example datasets for testing

These templates work with vanilla JavaScript, React, Vue, Svelte, or any other JavaScript environment. Adapt them as needed for your specific framework.

To use these resources, read the relevant files when detailed guidance is needed for specific visualisation types or patterns.

d3-viz

安装