mermaid/docs/syntax/stateDiagram.md

> **Warning**
>
> ## THIS IS AN AUTOGENERATED FILE. DO NOT EDIT.
>
> ## Please edit the corresponding file in [/packages/mermaid/src/docs/syntax/stateDiagram.md](../../packages/mermaid/src/docs/syntax/stateDiagram.md).

# State diagrams

> "A state diagram is a type of diagram used in computer science and related fields to describe the behavior of systems.
> State diagrams require that the system described is composed of a finite number of states; sometimes, this is indeed the
> case, while at other times this is a reasonable abstraction." Wikipedia

Mermaid can render state diagrams. The syntax tries to be compliant with the syntax used in plantUml as this will make
it easier for users to share diagrams between mermaid and plantUml.

```mermaid-example
---
title: Simple sample
---
stateDiagram-v2
    [*] --> Still
    Still --> [*]

    Still --> Moving
    Moving --> Still
    Moving --> Crash
    Crash --> [*]
```

```mermaid
---
title: Simple sample
---
stateDiagram-v2
    [*] --> Still
    Still --> [*]

    Still --> Moving
    Moving --> Still
    Moving --> Crash
    Crash --> [*]
```

Older renderer:

```mermaid-example
stateDiagram
    [*] --> Still
    Still --> [*]

    Still --> Moving
    Moving --> Still
    Moving --> Crash
    Crash --> [*]
```

```mermaid
stateDiagram
    [*] --> Still
    Still --> [*]

    Still --> Moving
    Moving --> Still
    Moving --> Crash
    Crash --> [*]
```

In state diagrams systems are described in terms of _states_ and how one _state_ can change to another _state_ via
a _transition._ The example diagram above shows three states: **Still**, **Moving** and **Crash**. You start in the
**Still** state. From **Still** you can change to the **Moving** state. From **Moving** you can change either back to the **Still** state or to
the **Crash** state. There is no transition from **Still** to **Crash**. (You can't crash if you're still.)

## States

A state can be declared in multiple ways. The simplest way is to define a state with just an id:

```mermaid-example
stateDiagram-v2
    stateId
```

```mermaid
stateDiagram-v2
    stateId
```

Another way is by using the state keyword with a description as per below:

```mermaid-example
stateDiagram-v2
    state "This is a state description" as s2
```

```mermaid
stateDiagram-v2
    state "This is a state description" as s2
```

Another way to define a state with a description is to define the state id followed by a colon and the description:

```mermaid-example
stateDiagram-v2
    s2 : This is a state description
```

```mermaid
stateDiagram-v2
    s2 : This is a state description
```

## Transitions

Transitions are path/edges when one state passes into another. This is represented using text arrow, "-->".

When you define a transition between two states and the states are not already defined, the undefined states are defined
with the id from the transition. You can later add descriptions to states defined this way.

```mermaid-example
stateDiagram-v2
    s1 --> s2
```

```mermaid
stateDiagram-v2
    s1 --> s2
```

It is possible to add text to a transition to describe what it represents:

```mermaid-example
stateDiagram-v2
    s1 --> s2: A transition
```

```mermaid
stateDiagram-v2
    s1 --> s2: A transition
```

## Start and End

There are two special states indicating the start and stop of the diagram. These are written with the \[\*] syntax and
the direction of the transition to it defines it either as a start or a stop state.

```mermaid-example
stateDiagram-v2
    [*] --> s1
    s1 --> [*]
```

```mermaid
stateDiagram-v2
    [*] --> s1
    s1 --> [*]
```

## Composite states

In a real world use of state diagrams you often end up with diagrams that are multidimensional as one state can
have several internal states. These are called composite states in this terminology.

In order to define a composite state you need to use the state keyword followed by an id and the body of the composite
state between {}. You can name a composite state on a separate line just like a simple state. See the example below:

```mermaid-example
stateDiagram-v2
    [*] --> First
    state First {
        [*] --> second
        second --> [*]
    }

    [*] --> NamedComposite
    NamedComposite: Another Composite
    state NamedComposite {
        [*] --> namedSimple
        namedSimple --> [*]
        namedSimple: Another simple
    }
```

```mermaid
stateDiagram-v2
    [*] --> First
    state First {
        [*] --> second
        second --> [*]
    }

    [*] --> NamedComposite
    NamedComposite: Another Composite
    state NamedComposite {
        [*] --> namedSimple
        namedSimple --> [*]
        namedSimple: Another simple
    }
```

You can do this in several layers:

```mermaid-example
stateDiagram-v2
    [*] --> First

    state First {
        [*] --> Second

        state Second {
            [*] --> second
            second --> Third

            state Third {
                [*] --> third
                third --> [*]
            }
        }
    }
```

```mermaid
stateDiagram-v2
    [*] --> First

    state First {
        [*] --> Second

        state Second {
            [*] --> second
            second --> Third

            state Third {
                [*] --> third
                third --> [*]
            }
        }
    }
```

You can also define transitions also between composite states:

```mermaid-example
stateDiagram-v2
    [*] --> First
    First --> Second
    First --> Third

    state First {
        [*] --> fir
        fir --> [*]
    }
    state Second {
        [*] --> sec
        sec --> [*]
    }
    state Third {
        [*] --> thi
        thi --> [*]
    }
```

```mermaid
stateDiagram-v2
    [*] --> First
    First --> Second
    First --> Third

    state First {
        [*] --> fir
        fir --> [*]
    }
    state Second {
        [*] --> sec
        sec --> [*]
    }
    state Third {
        [*] --> thi
        thi --> [*]
    }
```

_You can not define transitions between internal states belonging to different composite states_

## Choice

Sometimes you need to model a choice between two or more paths, you can do so using <\<choice>>.

```mermaid-example
stateDiagram-v2
    state if_state <<choice>>
    [*] --> IsPositive
    IsPositive --> if_state
    if_state --> False: if n < 0
    if_state --> True : if n >= 0
```

```mermaid
stateDiagram-v2
    state if_state <<choice>>
    [*] --> IsPositive
    IsPositive --> if_state
    if_state --> False: if n < 0
    if_state --> True : if n >= 0
```

## Forks

It is possible to specify a fork in the diagram using <\<fork>> <\<join>>.

```mermaid-example
   stateDiagram-v2
    state fork_state <<fork>>
      [*] --> fork_state
      fork_state --> State2
      fork_state --> State3

      state join_state <<join>>
      State2 --> join_state
      State3 --> join_state
      join_state --> State4
      State4 --> [*]
```

```mermaid
   stateDiagram-v2
    state fork_state <<fork>>
      [*] --> fork_state
      fork_state --> State2
      fork_state --> State3

      state join_state <<join>>
      State2 --> join_state
      State3 --> join_state
      join_state --> State4
      State4 --> [*]
```

## Notes

Sometimes nothing says it better than a Post-it note. That is also the case in state diagrams.

Here you can choose to put the note to the _right of_ or to the _left of_ a node.

```mermaid-example
    stateDiagram-v2
        State1: The state with a note
        note right of State1
            Important information! You can write
            notes.
        end note
        State1 --> State2
        note left of State2 : This is the note to the left.
```

```mermaid
    stateDiagram-v2
        State1: The state with a note
        note right of State1
            Important information! You can write
            notes.
        end note
        State1 --> State2
        note left of State2 : This is the note to the left.
```

## Concurrency

As in plantUml you can specify concurrency using the -- symbol.

```mermaid-example
stateDiagram-v2
    [*] --> Active

    state Active {
        [*] --> NumLockOff
        NumLockOff --> NumLockOn : EvNumLockPressed
        NumLockOn --> NumLockOff : EvNumLockPressed
        --
        [*] --> CapsLockOff
        CapsLockOff --> CapsLockOn : EvCapsLockPressed
        CapsLockOn --> CapsLockOff : EvCapsLockPressed
        --
        [*] --> ScrollLockOff
        ScrollLockOff --> ScrollLockOn : EvScrollLockPressed
        ScrollLockOn --> ScrollLockOff : EvScrollLockPressed
    }
```

```mermaid
stateDiagram-v2
    [*] --> Active

    state Active {
        [*] --> NumLockOff
        NumLockOff --> NumLockOn : EvNumLockPressed
        NumLockOn --> NumLockOff : EvNumLockPressed
        --
        [*] --> CapsLockOff
        CapsLockOff --> CapsLockOn : EvCapsLockPressed
        CapsLockOn --> CapsLockOff : EvCapsLockPressed
        --
        [*] --> ScrollLockOff
        ScrollLockOff --> ScrollLockOn : EvScrollLockPressed
        ScrollLockOn --> ScrollLockOff : EvScrollLockPressed
    }
```

## Setting the direction of the diagram

With state diagrams you can use the direction statement to set the direction which the diagram will render like in this
example.

```mermaid-example
stateDiagram
    direction LR
    [*] --> A
    A --> B
    B --> C
    state B {
      direction LR
      a --> b
    }
    B --> D
```

```mermaid
stateDiagram
    direction LR
    [*] --> A
    A --> B
    B --> C
    state B {
      direction LR
      a --> b
    }
    B --> D
```

## Comments

Comments can be entered within a state diagram chart, which will be ignored by the parser. Comments need to be on their
own line, and must be prefaced with `%%` (double percent signs). Any text after the start of the comment to the next
newline will be treated as a comment, including any diagram syntax

```mermaid-example
stateDiagram-v2
    [*] --> Still
    Still --> [*]
%% this is a comment
    Still --> Moving
    Moving --> Still %% another comment
    Moving --> Crash
    Crash --> [*]
```

```mermaid
stateDiagram-v2
    [*] --> Still
    Still --> [*]
%% this is a comment
    Still --> Moving
    Moving --> Still %% another comment
    Moving --> Crash
    Crash --> [*]
```

## Styling with classDefs

As with other diagrams (like flowcharts), you can define a style in the diagram itself and apply that named style to a
state or states in the diagram.

**These are the current limitations with state diagram classDefs:**

1. Cannot be applied to start or end states
2. Cannot be applied to or within composite states

_These are in development and will be available in a future version._

You define a style using the `classDef` keyword, which is short for "class definition" (where "class" means something
like a _CSS class_)
followed by _a name for the style,_
and then one or more _property-value pairs_. Each _property-value pair_ is
a _[valid CSS property name](https://www.w3.org/TR/CSS/#properties)_ followed by a colon (`:`) and then a _value._

Here is an example of a classDef with just one property-value pair:

```
    classDef movement font-style:italic;
```

where

- the _name_ of the style is `movement`
- the only _property_ is `font-style` and its _value_ is `italic`

If you want to have more than one _property-value pair_ then you put a comma (`,`) between each _property-value pair._

Here is an example with three property-value pairs:

```
    classDef badBadEvent fill:#f00,color:white,font-weight:bold,stroke-width:2px,stroke:yellow
```

where

- the _name_ of the style is `badBadEvent`
- the first _property_ is `fill` and its _value_ is `#f00`
- the second _property_ is `color` and its _value_ is `white`
- the third _property_ is `font-weight` and its _value_ is `bold`
- the fourth _property_ is `stroke-width` and its _value_ is `2px`
- the fifth _property_ is `stroke` and its _value_ is `yellow`

### Apply classDef styles to states

There are two ways to apply a `classDef` style to a state:

1. use the `class` keyword to apply a classDef style to one or more states in a single statement, or
2. use the `:::` operator to apply a classDef style to a state as it is being used in a transition statement (e.g. with an arrow
   to/from another state)

#### 1. `class` statement

A `class` statement tells Mermaid to apply the named classDef to one or more classes. The form is:

```txt
    class [one or more state names, separated by commas] [name of a style defined with classDef]
```

Here is an example applying the `badBadEvent` style to a state named `Crash`:

```txt
class Crash badBadEvent
```

Here is an example applying the `movement` style to the two states `Moving` and `Crash`:

```txt
class Moving, Crash movement
```

Here is a diagram that shows the examples in use. Note that the `Crash` state has two classDef styles applied: `movement`
and `badBadEvent`

```mermaid-example
   stateDiagram
   direction TB

   accTitle: This is the accessible title
   accDescr: This is an accessible description

   classDef notMoving fill:white
   classDef movement font-style:italic
   classDef badBadEvent fill:#f00,color:white,font-weight:bold,stroke-width:2px,stroke:yellow

   [*]--> Still
   Still --> [*]
   Still --> Moving
   Moving --> Still
   Moving --> Crash
   Crash --> [*]

   class Still notMoving
   class Moving, Crash movement
   class Crash badBadEvent
   class end badBadEvent
```

```mermaid
   stateDiagram
   direction TB

   accTitle: This is the accessible title
   accDescr: This is an accessible description

   classDef notMoving fill:white
   classDef movement font-style:italic
   classDef badBadEvent fill:#f00,color:white,font-weight:bold,stroke-width:2px,stroke:yellow

   [*]--> Still
   Still --> [*]
   Still --> Moving
   Moving --> Still
   Moving --> Crash
   Crash --> [*]

   class Still notMoving
   class Moving, Crash movement
   class Crash badBadEvent
   class end badBadEvent
```

#### 2. `:::` operator to apply a style to a state

You can apply a classDef style to a state using the `:::` (three colons) operator. The syntax is

```txt
[state]:::[style name]
```

You can use this in a diagram within a statement using a class. This includes the start and end states. For example:

```mermaid-example
stateDiagram
   direction TB

   accTitle: This is the accessible title
   accDescr: This is an accessible description

   classDef notMoving fill:white
   classDef movement font-style:italic;
   classDef badBadEvent fill:#f00,color:white,font-weight:bold,stroke-width:2px,stroke:yellow

   [*] --> Still:::notMoving
   Still --> [*]
   Still --> Moving:::movement
   Moving --> Still
   Moving --> Crash:::movement
   Crash:::badBadEvent --> [*]
```

```mermaid
stateDiagram
   direction TB

   accTitle: This is the accessible title
   accDescr: This is an accessible description

   classDef notMoving fill:white
   classDef movement font-style:italic;
   classDef badBadEvent fill:#f00,color:white,font-weight:bold,stroke-width:2px,stroke:yellow

   [*] --> Still:::notMoving
   Still --> [*]
   Still --> Moving:::movement
   Moving --> Still
   Moving --> Crash:::movement
   Crash:::badBadEvent --> [*]
```

## Spaces in state names

Spaces can be added to a state by first defining the state with an id and then referencing the id later.

In the following example there is a state with the id **yswsii** and description **Your state with spaces in it**.
After it has been defined, **yswsii** is used in the diagram in the first transition (`[*] --> yswsii`)
and also in the transition to **YetAnotherState** (`yswsii --> YetAnotherState`).
(**yswsii** has been styled so that it is different from the other states.)

```mermaid-example
stateDiagram
    classDef yourState font-style:italic,font-weight:bold,fill:white

    yswsii: Your state with spaces in it
    [*] --> yswsii:::yourState
    [*] --> SomeOtherState
    SomeOtherState --> YetAnotherState
    yswsii --> YetAnotherState
    YetAnotherState --> [*]
```

```mermaid
stateDiagram
    classDef yourState font-style:italic,font-weight:bold,fill:white

    yswsii: Your state with spaces in it
    [*] --> yswsii:::yourState
    [*] --> SomeOtherState
    SomeOtherState --> YetAnotherState
    yswsii --> YetAnotherState
    YetAnotherState --> [*]
```

<!--- cspell:ignore yswsii --->