initialize()

Configures Mermaid with global settings that apply to all diagrams. This method should be called before rendering any diagrams with run() or render().

Signature

function initialize(config: MermaidConfig): void

Parameters

config · MermaidConfig · required

Configuration object containing settings for Mermaid rendering.

Common configuration options:

Show properties

theme · string

The theme to use for rendering. Options: 'default', 'dark', 'forest', 'neutral', 'base'.

themeVariables · object

Override theme variables like colors and fonts.

fontFamily · string

Font family to use for all diagrams.

logLevel · string

Logging level. Options: 'debug', 'info', 'warn', 'error', 'fatal'.

securityLevel · string

Security level for rendering. Options: 'strict', 'loose', 'sandbox'.

startOnLoad · boolean

Whether to automatically render diagrams when the page loads.

maxTextSize · number

Maximum allowed text size for diagram definitions.

deterministicIds · boolean

Whether to use deterministic IDs for elements.

deterministicIDSeed · string

Seed for deterministic ID generation.

Return value

void - This method does not return a value.

Examples

Basic initialization

import mermaid from 'mermaid';

mermaid.initialize({
  theme: 'dark',
  logLevel: 'error',
  securityLevel: 'strict'
});

Custom theme configuration

mermaid.initialize({
  theme: 'base',
  themeVariables: {
    primaryColor: '#ff6b6b',
    primaryTextColor: '#fff',
    primaryBorderColor: '#ff6b6b',
    lineColor: '#f5a442',
    secondaryColor: '#4ecdc4',
    tertiaryColor: '#ffe66d'
  },
  fontFamily: 'Arial, sans-serif'
});

Configuration for automatic rendering

mermaid.initialize({
  startOnLoad: true,
  theme: 'default'
});

// Diagrams with class="mermaid" will be automatically rendered

Deterministic IDs for testing

mermaid.initialize({
  deterministicIds: true,
  deterministicIDSeed: 'test-seed'
});

Usage notes

• Call initialize() before using run() or render()
• Can be called multiple times to update configuration
• Configuration merges with existing settings
• When theme is specified, appropriate theme variables are automatically applied
• The fontFamily setting is propagated to themeVariables.fontFamily if not already set

Related methods

• run() - Render all diagrams on the page
• render() - Render a single diagram to SVG