mermaid-graph-renderer

Mermaid Graph Renderer

Renders Mermaid diagrams to production-quality SVG, PNG, and PDF in web and offline contexts. Covers the full spectrum from lazy-loaded client-side rendering to 1000x-faster native Rust batch export.

Core Constraint

Mermaid.js requires browser APIs (document.createElement, SVGTextElement.getBBox()) to compute text dimensions. Every non-browser rendering path must either embed a headless browser or reimplement the renderer from scratch. This constraint shapes every decision below.

When to Use

✅ Use for:

• Rendering Mermaid diagrams on web pages (performance-optimized)
• Exporting diagrams to SVG, PNG, or PDF (offline/CLI)
• Setting up CI/CD pipelines that generate diagram images
• Choosing between rendering libraries for a project
• Optimizing Mermaid load time on documentation sites

❌ NOT for:

• Writing Mermaid syntax (use mermaid-graph-writer)
• Rendering non-Mermaid formats (PlantUML, GraphViz — see Kroki)
• General image processing or manipulation

Rendering Decision Tree

flowchart TD
  A{Where are you rendering?} -->|Browser| B{Performance matters?}
  A -->|CLI / CI| C{Volume?}
  A -->|Server-side| D{Must avoid client JS?}

  B -->|Yes| E[Lazy-load mermaid.js]
  B -->|No| F[CDN script tag]

  C -->|1-10 diagrams| G[mermaid-cli]
  C -->|10-100 diagrams| H{Need multiple formats?}
  C -->|100+ diagrams| I[mmdr Rust renderer]

  H -->|Mermaid only| G
  H -->|Multiple languages| J[Kroki]

  D -->|Yes, zero JS| K[Build-time with Puppeteer]
  D -->|Some JS OK| E
  K -->|Slow builds warning| L[rehype-mermaid + Playwright]

Web Rendering

Option 1: Lazy-Loaded mermaid.js (Recommended)

Best for documentation sites, blogs, and apps where only some pages have diagrams.

How it works: Check for .mermaid elements before loading the library. The ~480 KB cost is only paid on pages that actually need it.

// Lazy load pattern — only loads mermaid.js when diagrams exist
function initMermaid() {
  const diagrams = document.querySelectorAll('.mermaid');
  if (diagrams.length === 0) return;

  const script = document.createElement('script');
  script.src = 'https://cdn.jsdelivr.net/npm/mermaid@11/dist/mermaid.min.js';
  script.onload = () => {
    mermaid.initialize({ startOnLoad: false, theme: 'neutral' });
    mermaid.run({ nodes: diagrams });
  };
  document.head.appendChild(script);
}

// Handle initial load + SPA navigation
document.addEventListener('DOMContentLoaded', initMermaid);
// For SPA route changes: call initMermaid() after navigation