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MermaidJS - Diagramming and Charting Tool

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What is MermaidJS?

MermaidJS is an open-source JavaScript library that generates diagrams and charts from text-based definitions. It uses a simple markup language similar to Markdown to create various types of visualizations directly in documentation and web pages.

Key Features

  • 📝 Text-based syntax - Define diagrams using simple code
  • 🎨 Multiple diagram types - Supports 10+ different diagram styles
  • 🌐 Browser & Node.js support - Works in both client and server environments
  • 🔄 Live editors - Built-in editors for real-time preview
  • 🤝 Integration - Works with popular tools like GitHub, GitLab, and VS Code

Supported Diagram Types

Diagram Type Description
Flowchart Process flows and workflows
Sequence Diagram System interactions over time
Class Diagram Object-oriented class structures
State Diagram State machines and transitions
Entity Relationship Database relationships
User Journey User experience flows
Gantt Chart Project timelines and schedules
Pie Chart Proportional data representation
Quadrant Chart 2x2 comparison matrices
Requirement Diagram System requirements visualization

Basic Syntax Examples

Flowchart

flowchart TD
    A[Start] --> B{Decision}
    B -->|Yes| C[Action 1]
    B -->|No| D[Action 2]
    C --> E[End]
    D --> E

flowchart TD A[Start] --> B{Decision} B -->|Yes| C[Action 1] B -->|No| D[Action 2] C --> E[End] D --> E

Sequence Diagram

sequenceDiagram
    Alice->>John: Hello John!
    John-->>Alice: Hi Alice!
    Alice->>John: How are you?
    John-->>Alice: I'm good!

sequenceDiagram Alice->>John: Hello John! John-->>Alice: Hi Alice! Alice->>John: How are you? John-->>Alice: I'm good!

Benefits

  1. Version Control Friendly - Diagrams as code can be tracked in Git
  2. Accessibility - Text-based format works with screen readers
  3. Maintainability - Easier to update than image-based diagrams
  4. Collaboration - Changes can be reviewed in pull requests

Use Cases

  • Technical documentation
  • System design planning
  • API documentation
  • Project management
  • Educational materials
  • Presentation slides

Getting Started

  1. Include Mermaid in your HTML:
<script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/mermaid.min.js"></script>
  1. Initialize with:
mermaid.initialize({ startOnLoad: true });
  1. Create a diagram container:
<div class="mermaid">
    graph TD
    A --> B
</div>

Customization & Theming

Mermaid supports extensive customization through:

  • Built-in themes (default, dark, forest, neutral)
  • CSS styling overrides
  • Configuration options for:
    • Font styles
    • Arrow types
    • Node spacing
    • Color schemes

Integration Options

  • GitHub/Markdown (native support in GitHub repositories)
  • VS Code (via Mermaid extension)
  • Docusaurus (official plugin)
  • React (mermaid-react component)
  • Jupyter Notebooks (mermaid-js extension)

Limitations

  • Steep learning curve for complex diagrams
  • Limited graphical customization compared to dedicated tools
  • Text formatting constraints
  • Complex layouts can become difficult to manage

Resources