mermaid-isomorphic

Render Mermaid diagrams in the browser or Node.js.

This is useful if you wish to render Mermaid diagrams in a Node.js or an isomorphic environment. If you want to render Mermaid diagrams in the browser directly, use the mermaid package directly.

Installation

npm install mermaid-isomorphic

Outside of browsers mermaid-isomorphic uses Playwright. If you use this outside of a browser, you need to install Playwright and a Playwright browser.

npm install playwright
npx playwright install --with-deps chromium

Usage

First, create a Mermaid renderer. Then use this renderer to render your diagrams.

import { createMermaidRenderer } from 'mermaid-isomorphic'

const renderer = createMermaidRenderer()
const diagram = `
graph TD;
    A-->B;
    A-->C;
    B-->D;
    C-->D;
`

const results = await renderer([diagram])
console.log(results)

Fonts

FontAwesome

Mermaid has support for FontAwesome. This is also supported by isomorphic-mermaid, but you need to load the FontAwesome CSS yourself when serving the SVG.

Custom Fonts

By default mermaid-isomorphic uses the arial,sans-serif font family. This font family is mostly compatible across all browsers and devices. If you wish to use a custom font, you need to specify both the mermaidConfig.fontFamily and css options.

Browser

mermaid-isomorphic is intended for use in Node.js, but also provides a browser export. This means it can be used in the browser, but it’s recommended to use the mermaid package directly.

API

`createMermaidRenderer(options?: CreateMermaidRendererOptions)`

Create a Mermaid renderer.

The Mermaid renderer manages a browser instance. If multiple diagrams are being rendered simultaneously, the internal browser instance will be re-used. If no diagrams are being rendered, the browser will be closed.

Options

browserType (BrowserType): The Playwright browser to use. (default: chromium)
launchOptions: (LaunchOptions): The options used to launch the browser.

Returns

A function that renders Mermaid diagrams in the browser. This function has arguments:

diagrams (string[]): An array of mermaid diagrams to render.
options:
- css (string | URL) A URL that points to a custom CSS file to load. Use this to load custom
  fonts. This option is ignored in the browser. You need to include the CSS in your build
  manually.
- screenshot (boolean): If true, a PNG screenshot of the diagram is included as a buffer. This
  is only supported in Node.js.
- prefix (string): A custom prefix to use for Mermaid IDs (default: mermaid).
- mermaidOptions (MermaidConfig): A custom Mermaid configuration. By default fontFamily is
  set to arial,sans-serif. This option is ignored in the browser. You need to call
  mermaid.initialize() manually.

It returns a promise settled result with the render results. The render results have the following properties:

description (string): The aria description of the diagram, if it has one.
height (number): The height of the resulting SVG.
id (string): The DOM id of the SVG node.
screenshot (Buffer): The diagram SVG rendered as a PNG buffer. This is only added if the
screenshot option is true.
svg (string): The diagram rendered as an SVG.
title (string): The title of the rendered diagram, if it has one.
width (number): The width of the resulting SVG.

Compatibility

This project is compatible with Node.js 18 or greater.

Contributing

Test fixtures are generated and verified using Linux. Rendering on other platforms may yield slightly different results. Don’t worry about adding new fixtures, but don’t update existing ones that cause CI to fail. Furthermore see my global contributing guidelines.