Usage

Installation

npm package

yarn add mermaid

CDN

https://unpkg.com/mermaid/

Please note that you can switch versions through the dropdown box on top right.

Simple usage on a web page

The easiest way to integrate mermaid on a web page requires two elements:

  1. Inclusion of the mermaid framework in the html page using a script tag
  2. A graph definition on the web page

If these things are in place mermaid listens to the page load event and when fires, when the page has loaded, it will locate the graphs n the page and transform them to svg files.

Include mermaid on your web page:

<script src="mermaid.min.js"></script>
<script>mermaid.initialize({startOnLoad:true});</script>

Further down on your page mermaid will look for tags with class="mermaid". From these tags mermaid will try to read the chart definiton which will be replaced with the svg chart.

Define a chart like this:

<div class="mermaid">
    CHART DEFINITION GOES HERE
</div>

Would end up like this:

<div class="mermaid" id="mermaidChart0">
    <svg>
        Chart ends up here
    </svg>
</div>

An id is also added to mermaid tags without id.

Simple full example:

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <link rel="stylesheet" href="mermaid.min.css">
</head>
<body>
  <div class="mermaid">
  graph LR
      A --- B
      B-->C[fa:fa-ban forbidden]
      B-->D(fa:fa-spinner);
  </div>
  <script src="mermaid.min.js"></script>
  <script>mermaid.initialize({startOnLoad:true});</script>
</body>
</html>

Labels out of bounds

If you use dynamically loaded fonts that are loaded through CSS, such as Google fonts, mermaid should wait for the whole page to have been loaded (dom + assets, particularly the fonts file).

$(document).load(function() {
    mermaid.initialize();
});

over

$(document).ready(function() {
    mermaid.initialize();
});

Not doing so will most likely result in mermaid rendering graphs that have labels out of bounds. The default integration in mermaid uses the window.load event to start rendering.

Calling mermaid.init

By default, mermaid.init will be called when the document is ready, finding all elements with class="mermaid". If you are adding content after mermaid is loaded, or otherwise need finer-grained control of this behavior, you can call init yourself with:

  • a configuration object
  • some nodes, as
    • a node
    • an a array-like of nodes
    • or W3C selector that will find your nodes

Example:

mermaid.init({noteMargin: 10}, ".someOtherClass");

Or with no config object, and a jQuery selection:

mermaid.init(undefined, $("#someId .yetAnotherClass"));

This type of integration is deprecated instead the preferred way of handling more complex integration is to us the mermaidAPI instead.

Usage with webpack

mermaid fully supports webpack. Here is a working demo.

API usage

The main idea with the API is to be able to call a render function with graph defintion as a string. The render function will render the graph and call a callback with the resulting svg code. With this approach it is up to the site creator to fetch the graph definition from the site, perhaps from a textarea, render it and place the graph somewhere in the site.

To do this, include mermaidAPI on your web website instead of mermaid.js. The example below show an outline of how this could be used. The example just logs the resulting svg to the javascript console.

<script src="mermaidAPI.js"></script>

<script>
    mermaidAPI.initialize({
        startOnLoad:false
    });
    $(function(){
        // Example of using the API
        var element = document.querySelector("#graphDiv");

        var insertSvg = function(svgCode, bindFunctions){
            element.innerHTML = svgCode;
        };

        var graphDefinition = 'graph TB\na-->b';
        var graph = mermaidAPI.render('graphDiv', graphDefinition, insertSvg);
    });
</script>

Binding events

Sometimes the generated graph also has defined interactions like tooltip and click events. When using the API one must add those events after the graph has been inserted into the DOM.

The example code below is an extract of wheat mermaid does when using the API. The example show how it is possible to bind events to a svg when using the API for rendering.

var insertSvg = function(svgCode, bindFunctions) {
    element.innerHTML = svgCode;
    if(typeof callback !== 'undefined'){
        callback(id);
    }
    bindFunctions(element);
};

var id = 'theGraph';


mermaidAPI.render(id,txt,insertSvg, element);
  1. The graph is generated using the render call.
  2. After generation the render function calls the provided callback function, in this case its called insertSvg.
  3. The callback function is called with two parameters, the svg code of the generated graph and a function. This function binds events to the svg after it is inserted into the DOM.
  4. Insert the svg code into the DOM for presentation
  5. Call the binding function that bainds the events

Example of a marked renderer

This is the renderer used for transforming the documentation from markdown to html with mermaid diagrams in the html.

var renderer = new marked.Renderer();
renderer.code = function (code, language) {
    if(code.match(/^sequenceDiagram/)||code.match(/^graph/)){
        return '<div class="mermaid">'+code+'</div>';
    }
    else{
        return '<pre><code>'+code+'</code></pre>';
    }
};

Another example in coffeescript that also includes the mermaid script tag into the generated markup.

marked = require 'marked'

module.exports = (options) ->
  hasMermaid = false
  renderer = new marked.Renderer()
  renderer.defaultCode = renderer.code
  renderer.code = (code, language) ->
    if language is 'mermaid'
      html = ''
      if not hasMermaid
        hasMermaid = true
        html += '<script src="'+options.mermaidPath+'"></script>'
      html + '<div class="mermaid">'+code+'</div>'
    else
      @defaultCode(code, language)

  renderer

Advanced usage

Error handling

When the parser encounters invalid syntax the mermaid.parseError function is called. It is possible to override this function in order to handle the error in an application specific way.

Parsing text without rendering

It is also possible to validate the syntax before rendering in order to streamline the user experience. The function mermaid.parse(txt) takes a text string as an argument and returns true if the text is syntactically correct and false if it is not. The parseError function will be called when the parse function returns false.

The code-example below in meta code illustrates how this could work:

mermaid.parseError = function(err,hash){
    displayErrorInGui(err);
};

var textFieldUpdated = function(){
    var textStr = getTextFromFormField('code');

    if(mermaid.parse(textStr)){
        reRender(textStr)
    }
};

bindEventHandler('change', 'code', textFieldUpdated);

Configuration

Mermaid takes a number of options which lets you tweak the rendering of the diagrams. Currently there are three ways of setting the options in mermaid.

  1. Instantiation of the configuration using the initialize call
  2. Using the global mermaid object - deprecated
  3. using the global mermaid_config object - deprecated
  4. Instantiation of the configuration using the mermaid.init call

The list above has two ways to many of doing this. Three are deprecated and will eventually be removed. The list of configuration objects are described in the mermaidAPI documentation.

Using the mermaidAPI.initialize/mermaid.initialize call

The future proof way of setting the configuration is by using the initialization call to mermaid or mermaidAPi depending on what kind of integration you use.

<script src="../dist/mermaid.js"></script>
<script>
    var config = {
        startOnLoad:true,
        flowchart:{
            useMaxWidth:false,
            htmlLabels:true
        }
    };
    mermaid.initialize(config);
</script>

This is the preferred way of configuring mermaid.

Using the mermaid object

Is it possible to set some configuration via the mermaid object. The two parameters that are supported using this approach are:

  • mermaid.startOnLoad
  • mermaid.htmlLabels
mermaid.startOnLoad = true;

This way of setting the configuration is deprecated instead the preferred way of is to use the initialize method. This functionality is only kept for not breaking existing integrations

Using the mermaid_config

Is it possible to set some configuration via the mermaid object. The two parameters that are supported using this approach are:

  • mermaid_config.startOnLoad
  • mermaid_config.htmlLabels
mermaid_config.startOnLoad = true;

This way of setting the configuration is deprecated instead the preferred way of is to use the initialize method. This functionality is only kept for not breaking existing integrations

Using the mermaid.init call

Is it possible to set some configuration via the mermaid object. The two parameters that are supported using this approach are:

  • mermaid_config.startOnLoad
  • mermaid_config.htmlLabels
mermaid_config.startOnLoad = true;

This way of setting the configuration is deprecated instead the preferred way of is to use the initialize method. This functionality is only kept for not breaking existing integrations

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