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Directives

Directives

Directives gives a diagram author the capability to alter the appearance of a diagram before rendering by changing the applied configuration.

The significance of having directives is that you have them available while writing the diagram, and can modify the default global and diagram specific configurations. So, directives are applied on top of the default configurations. The beauty of directives is that you can use them to alter configuration settings for a specific diagram, i.e. at an individual level.

While directives allow you to change most of the default configuration settings, there are some that are not available, that too for security reasons. Also, you do have the option to define the set of configurations that you would allow to be available to the diagram author for overriding with help of directives.

Types of Directives options

Mermaid basically supports two types of configuration options to be overridden by directives.

  1. General/Top Level configurations : These are the configurations that are available and applied to all the diagram. Some of the most important top-level configurations are:
  • theme
  • fontFamily
  • logLevel
  • securityLevel
  • startOnLoad
  • secure
  1. Diagram specific configurations : These are the configurations that are available and applied to a specific diagram. For each diagram there are specific configuration that will alter how that particular diagram looks and behaves. For example, mirrorActors is a configuration that is specific to the SequenceDiagram and alter whether the actors are mirrored or not. So this config is available only for the SequenceDiagram type.

NOTE: These options listed here are not all the configuration options. To get hold of all the configuration options, please refer to the defaultConfig.ts in the source code.

Soon we plan to publish a complete list of top-level configurations & all the diagram specific configurations, with their possible values in the docs

Declaring directives

Now that we have defined the types of configurations that are available, we can learn how to declare directives. A directive always starts and end %% sign with directive text in between, like %% {directive_text} %%.

Here the structure of a directive text is like a nested key-value pair map or a JSON object with root being init. Where all the general configurations are defined in the top level, and all the diagram specific configurations are defined one level deeper with diagram type as key/root for that section.

Following code snippet shows the structure of a directive:

%%{
  init: {
    "theme": "dark",
    "fontFamily": "monospace",
    "logLevel": "info",
    "flowchart": {
      "htmlLabels": true,
      "curve": "linear"
    },
    "sequence": {
      "mirrorActors": true
    }
  }
}%%

You can also define the directives in a single line, like this:

%%{init: { **insert argument here**}}%%

For example, the following code snippet:

%%{init: { "sequence": { "mirrorActors":false }}}%%

Notes: The json object that is passed as {argument } must be valid key value pairs and encased in quotation marks or it will be ignored. Valid Key Value pairs can be found in config.

Example with a simple graph:

Code:
mermaid
%%{init: { 'logLevel': 'debug', 'theme': 'dark' } }%%
graph LR
A-->B
null

Here the directive declaration will set the logLevel to debug and the theme to dark for a rendered mermaid diagram, changing the appearance of the diagram itself.

Note: You can use 'init' or 'initialize' as both acceptable as init directives. Also note that %%init%% and %%initialize%% directives will be grouped together after they are parsed. This means:

Code:
mermaid
%%{init: { 'logLevel': 'debug', 'theme': 'forest' } }%%
%%{initialize: { 'logLevel': 'fatal', "theme":'dark', 'startOnLoad': true } }%%
...
null

parsing the above generates a single %%init%% JSON object below, combining the two directives and carrying over the last value given for loglevel:

json
{
  "logLevel": "fatal",
  "theme": "dark",
  "startOnLoad": true
}

This will then be sent to mermaid.initialize(...) for rendering.

Directive Examples

More directive examples for diagram specific configuration overrides Now that the concept of directives has been explained, Let us see some more examples for directives usage:

Changing Theme via directive

The following code snippet changes theme to forest:

%%{init: { "theme": "forest" } }%%

Possible themes value are: default,base, dark, forest and neutral. Default Value is default.

Example:

Code:
mermaid
%%{init: { "theme": "forest" } }%%
graph TD
A(Forest) --> B[/Another/]
A --> C[End]
  subgraph section
  B
  C
  end

null

Changing fontFamily via directive

The following code snippet changes fontFamily to rebuchet MS, Verdana, Arial, Sans-Serif:

%%{init: { "fontFamily": "Trebuchet MS, Verdana, Arial, Sans-Serif" } }%%

Example:

Code:
mermaid
%%{init: { "fontFamily": "Trebuchet MS, Verdana, Arial, Sans-Serif" } }%%
graph TD
A(Forest) --> B[/Another/]
A --> C[End]
  subgraph section
  B
  C
  end

null

Changing logLevel via directive

The following code snippet changes logLevel to 2:

%%{init: { "logLevel": 2 } }%%

Possible logLevel values are:

  • 1 for debug,
  • 2 for info
  • 3 for warn
  • 4 for error
  • 5 for only fatal errors

Default Value is 5.

Example:

Code:
mermaid
%%{init: { "logLevel": 2 } }%%
graph TD
A(Forest) --> B[/Another/]
A --> C[End]
  subgraph section
  B
  C
  end
null

Changing flowchart config via directive

Some common flowchart configurations are:

  • htmlLabels: true/false
  • curve: linear/curve
  • diagramPadding: number
  • useMaxWidth: number

For complete list of flowchart configurations, see defaultConfig.ts in the source code. Soon we plan to publish a complete list all diagram specific configurations updated in the docs

The following code snippet changes flowchart config:

%%{init: { "flowchart": { "htmlLabels": true, "curve": "linear" } } }%%

Here were are overriding only the flowchart config, and not the general config, where HtmlLabels is set to true and curve is set to linear.

Code:
mermaid
%%{init: { "flowchart": { "htmlLabels": true, "curve": "linear" } } }%%
graph TD
A(Forest) --> B[/Another/]
A --> C[End]
  subgraph section
  B
  C
  end
null

Changing Sequence diagram config via directive

Some common sequence configurations are:

  • width: number
  • height: number
  • messageAlign: left, center, right
  • mirrorActors: boolean
  • useMaxWidth: boolean
  • rightAngles: boolean
  • showSequenceNumbers: boolean
  • wrap: boolean

For complete list of sequence diagram configurations, see defaultConfig.ts in the source code. Soon we plan to publish a complete list all diagram specific configurations updated in the docs

So, wrap by default has a value of false for sequence diagrams.

Let us see an example:

Code:
mermaid
sequenceDiagram

Alice->Bob: Hello Bob, how are you?
Bob->Alice: Fine, How did you mother like the book I suggested? And did you catch with the new book about alien invasion?
Alice->Bob: Good.
Bob->Alice: Cool
null

Now let us enable wrap for sequence diagrams.

The following code snippet changes sequence diagram config for wrap to true:

%%{init: { "sequence": { "wrap": true} } }%%

Using in the diagram above, the wrap will be enabled.

Code:
mermaid
%%{init: { "sequence": { "wrap": true, "width":300 } } }%%
sequenceDiagram
Alice->Bob: Hello Bob, how are you?
Bob->Alice: Fine, How did you mother like the book I suggested? And did you catch with the new book about alien invasion?
Alice->Bob: Good.
Bob->Alice: Cool
null