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devinoue/type-mermaid

Mermaid generator typed in TypeScript

diagramdiagram-generatormermaidmermaidjstypescript

type-mermaid Build Test

A library for writing Mermaid code in TypeScript.
With this library, you can easily write Mermaid code using TypeScript and IDE IntelliSense.

Currently, only sequence diagrams are supported.

NPM

Try it out for yourself

Open in StackBlitz

Installing

For the latest stable version, run:

# NPM
npm i type-mermaid

# or Yarn
yarn add type-mermaid

Requirements

  • Typescript >=4.9

Be careful with the TypeScript version because it uses the satisfies operator.

Usage

Simple Mermaid code output

import { SequenceDiagram, MemberObject } from 'type-mermaid'

const member = {
  Alice: 'participant',
  Bob: 'participant',
} satisfies MemberObject

const { d, render } = SequenceDiagram<keyof typeof member>(member)

// Morning greetings
d.Alice.call.Bob.activate('Good morning, Bob!')
d.Bob.response.Alice.msg('Morning, Alice')

// console output
console.log(render.toString())

The basic flow is to use a d object (which stands for diagram) to create flow, and then use a render instance to output mermaid code or image.

Output

sequenceDiagram
    participant Alice
    participant Bob
    Alice->>Bob: Good morning, Bob!
    Bob-->>Alice: Morning, Alice

and Mermaid preview.

sequenceDiagram
    participant Alice
    participant Bob
    Alice->>Bob: Good morning, Bob!
    Bob-->>Alice: Morning, Alice
Loading

SVG output

Using render instance, SVG files can also be output.

const svgPath = path.join(__dirname, './test.svg')
render.toSvg(svgPath)

MMD file output

const mmdPath = path.join(__dirname, './test.mmd')
render.toMmd(mmdPath)

Options

Options for auto numbering(autonumber) and indentation can be specified as a string.
By default, indentation is four spaces.

Example

import { SequenceDiagram } from '../SequenceDiagram'
import { MemberObject } from '../SequenceDiagram/types'

import path from 'path'

const member = {
  Alice: 'participant',
  Bob: 'participant',
} satisfies MemberObject

const options = {
  autoNumber: true,
  indent: '  ',  //two spaces
}

const { d, render } = SequenceDiagram<keyof typeof member>(member, options)

// Morning greetings
d.Alice.call.Bob.activate('Good morning, Bob!')
d.Bob.response.Alice.msg('Morning, Alice')

console.log(render.toString())

Output

sequenceDiagram
  autonumber
  participant Alice
  participant Bob
  Alice->>+Bob: Good morning, Bob!
  Bob-->>Alice: Morning, Alice

by Mermaid

sequenceDiagram
  autonumber
  participant Alice
  participant Bob
  Alice->>+Bob: Good morning, Bob!
  Bob-->>Alice: Morning, Alice
Loading

Activation

There are two ways to express Activation.

1. Declare activate first and code the sequence of events in then().

In this case, this code will automatically output without writing deactivate.

Example

d.Alice.call.Bob.msg('Do you have the documents?')
d.activate.Bob.then(() => {
  d.Bob.call.Bob.msg('Thinking...')
  d.Bob.response.Alice.msg('I have it!')
})

Output

sequenceDiagram
    participant Alice
    participant Bob
    Alice->>Bob: Do you have the documents?
    activate Bob
    Bob->>Bob: Thinking...
    Bob-->>Alice: I have it!
    deactivate Bob

sequenceDiagram
    participant Alice
    participant Bob
    Alice->>Bob: Do you have the documents?
    activate Bob
    Bob->>Bob: Thinking...
    Bob-->>Alice: I have it!
    deactivate Bob
Loading

2. Send a message and activate at the same time.

In this case, use the activate() to send a message. Then you must always use the deactivate() to terminate the activation.

Example

d.Alice.call.Bob.activate('Do you have the documents?')
d.Bob.call.Bob.msg('Thinking...')
d.Bob.response.Alice.deactivate("I've got it!")

Output

sequenceDiagram
    participant Alice
    participant Bob
    Alice->>+Bob: Do you have the documents?
    Bob->>Bob: Thinking...
    Bob-->>-Alice: I've got it!

sequenceDiagram
    participant Alice
    participant Bob
    Alice->>+Bob: Do you have the documents?
    Bob->>Bob: Thinking...
    Bob-->>-Alice: I've got it!
Loading

Notes

It is possible to add notes to a sequence diagram.

Example

d.note.rightOf.Alice.msg('Text in note')

Output

sequenceDiagram
    participant Alice
    Note right of Alice: Text in note

sequenceDiagram
    participant Alice
    Note right of Alice: Text in note
Loading

To create notes spanning two participants.

d.Alice.call.Bob.msg('Hello Bob, how are you?')
d.note.over.Alice.Bob.msg('A typical interaction')

Output

sequenceDiagram
    participant Alice
    participant Bob
    Alice->>Bob: Hello Bob, how are you?
    Note over Alice,Bob: A typical interaction

sequenceDiagram
    participant Alice
    participant Bob
    Alice->>Bob: Hello Bob, how are you?
    Note over Alice,Bob: A typical interaction
Loading

Loops

It is possible to express loops in a sequence diagram.

Example

d.Alice.call.Bob.msg('Hello Bob, how are you?')
d.loop.then('Every minute', () => {
  d.Bob.response.Alice.msg('Great!')
})

In then(), enter a label and a sequence to repeat.
If no label is needed, the first argument will be an empty character ('').

Output

sequenceDiagram
    participant Alice
    participant Bob
    Alice->>Bob: Hello Bob, how are you?
    loop Every minute
        Bob-->>Alice: Great!
    end

sequenceDiagram
    participant Alice
    participant Bob
    Alice->>Bob: Hello Bob, how are you?
    loop Every minute
        Bob-->>Alice: Great!
    end
Loading

Alt and Opt

It is possible to express alternative paths in a sequence diagram.

Example

// Alt
d.Alice.call.Bob.msg('Hello Bob, how are you?')
d.alt.then('is sick', () => {
  d.Bob.response.Alice.msg('Not so good :(')
  d.else.then('is well', () => {
    d.Bob.response.Alice.msg('Feeling fresh like a daisy')
  })
})

// Opt
d.opt.then('Extra response', () => {
  d.Bob.response.Alice.msg('Thanks for asking')
})

Output

sequenceDiagram
    participant Alice
    participant Bob
    Alice->>Bob: Hello Bob, how are you?
    alt is sick
        Bob-->>Alice: Not so good :(
    else is well
        Bob-->>Alice: Feeling fresh like a daisy
    end
    opt Extra response
        Bob-->>Alice: Thanks for asking
    end

sequenceDiagram
    participant Alice
    participant Bob
    Alice->>Bob: Hello Bob, how are you?
    alt is sick
        Bob-->>Alice: Not so good :(
    else is well
        Bob-->>Alice: Feeling fresh like a daisy
    end
    opt Extra response
        Bob-->>Alice: Thanks for asking
    end
Loading

Parallel

It is possible to show actions that are happening in parallel.

Example

// add John
const member = {
  Alice: 'participant',
  Bob: 'participant',
  John: 'participant',
} satisfies MemberObject

const { d, render } = SequenceDiagram<keyof typeof member>(member)

d.par.then('Alice to Bob', () => {
  d.Alice.call.Bob.msg('Hello guys!')
  d.and.then('Alice to John', () => {
    d.Alice.call.John.msg('Hello guys!')
  })
})
d.Bob.response.Alice.msg('Hi Alice!')
d.John.response.Alice.msg('Hi Alice!')

and.then() should be used within a callback function for then()'s second argument.

Multiple and.then() can be used.

Output

sequenceDiagram
    participant Alice
    participant Bob
    participant John
    par Alice to Bob
        Alice->>Bob: Hello guys!
    and Alice to John
        Alice->>John: Hello guys!
    end
    Bob-->>Alice: Hi Alice!
    John-->>Alice: Hi Alice!
Loading 
sequenceDiagram
    participant Alice
    participant Bob
    participant John
    par Alice to Bob
        Alice->>Bob: Hello guys!
    and Alice to John
        Alice->>John: Hello guys!
    end
    Bob-->>Alice: Hi Alice!
    John-->>Alice: Hi Alice!
Loading

It is also possible to nest parallel blocks.

Example

const member = {
  Alice: 'participant',
  Bob: 'participant',
  John: 'participant',
  Charlie: 'participant',
  Diana: 'participant',
} satisfies MemberObject

const { d, render } = SequenceDiagram<keyof typeof member>(member)

d.par.then('Alice to Bob', () => {
  d.Alice.call.Bob.msg('Go help John')
  d.and.then('Alice to John', () => {
    d.Alice.call.John.msg('I want this done today')
    d.par.then('John to Charlie', () => {
      d.John.call.Charlie.msg('Can we do this today?')
      d.and.then('John to Diana', () => {
        d.John.call.Diana.msg('Can you help us today?')
      })
    })
  })
})

All participants must be defined by member. Otherwise, an error will occur.

(Because this is TypeScript!).

Output

sequenceDiagram
    participant Alice
    participant Bob
    participant John
    participant Charlie
    participant Diana
    par Alice to Bob
        Alice->>Bob: Go help John
    and Alice to John
        Alice->>John: I want this done today
        par John to Charlie
            John->>Charlie: Can we do this today?
        and John to Diana
            John->>Diana: Can you help us today?
        end
    end
Loading 
sequenceDiagram
    participant Alice
    participant Bob
    participant John
    participant Charlie
    participant Diana
    par Alice to Bob
        Alice->>Bob: Go help John
    and Alice to John
        Alice->>John: I want this done today
        par John to Charlie
            John->>Charlie: Can we do this today?
        and John to Diana
            John->>Diana: Can you help us today?
        end
    end
Loading

Critical Region

It is possible to show actions that must happen automatically with conditional handling of circumstances.

Example

const member = {
  Service: 'participant',
  DB: 'participant',
} satisfies MemberObject

d.critical.then('critical Establish a connection to the DB', () => {
  d.Service.call.DB.msg('connect')
  d.optionWhenCritical.then('Network timeout', () => {
    d.Service.response.Service.msg('Log error')
  })
  d.optionWhenCritical.then('Credentials rejected', () => {
    d.Service.response.Service.msg('Log different error')
  })
})

Output

sequenceDiagram
    participant Service
    participant DB
    critical critical Establish a connection to the DB
        Service->>DB: connect
    option Network timeout
        Service-->>Service: Log error
    option Credentials rejected
        Service-->>Service: Log different error
    end
Loading

Break

It is possible to indicate a stop of the sequence within the flow (usually used to model exceptions).

Example

const member = {
  Consumer: 'participant',
  API: 'participant',
  BookingService: 'participant',
  BillingService: 'participant',
} satisfies MemberObject

const { d, render } = SequenceDiagram<keyof typeof member>(member)

d.Consumer.dotted.API.msg('Book something')
d.API.dotted.BookingService.msg('Start booking process')
d.breakWhen.then('when the booking process fails', () => {
  d.API.dotted.Consumer.msg('show failure')
})
d.API.dotted.BillingService.msg('Start billing process')

Output

sequenceDiagram
    Consumer-->API: Book something
    API-->BookingService: Start booking process
    break when the booking process fails
        API-->Consumer: show failure
    end
    API-->BillingService: Start billing process
Loading

Background Highlighting

It is possible to highlight flows by providing colored background rects. This is done by the notation

The colors are defined using rgb and rgba syntax.

Example

const member = {
  Alice: 'participant',
  John: 'participant',
} satisfies MemberObject

const { d, render } = SequenceDiagram<keyof typeof member>(member)
d.rect.then('rgb(191, 223, 255)', () => {
  d.note.rightOf.Alice.msg('Alice calls John.')
  d.Alice.call.John.activate('Hello John, how are you?')
  d.rect.then('rgb(200, 150, 255)', () => {
    d.Alice.call.John.activate('John, can you hear me?')
    d.John.response.Alice.deactivate('Hi Alice, I can hear you!')
  })
  d.John.response.Alice.deactivate('I feel great!')
})
d.Alice.call.John.activate('Did you want to go to the game tonight?')
d.John.response.Alice.deactivate('Yeah! See you there.')

Output

sequenceDiagram
    participant Alice
    participant John
    rect rgb(191, 223, 255)
        Note right of Alice: Alice calls John.
        Alice->>+John: Hello John, how are you?
        rect rgb(200, 150, 255)
            Alice->>+John: John, can you hear me?
            John-->>-Alice: Hi Alice, I can hear you!
        end
        John-->>-Alice: I feel great!
    end
    Alice->>+John: Did you want to go to the game tonight?
    John-->>-Alice: Yeah! See you there.
Loading

That's it!

Languages

TypeScript87.0%JavaScript13.0%

Contributors

DE
MIT License
Created December 31, 2022
Updated August 7, 2025
devinoue/type-mermaid | GitHunt