MiddleState

An intermediate transition state. Represents “in the process of going from oldState via action toward newState”.

Definition

export class MiddleState {
  oldState: State
  newState: string
  action: string
  aborted: boolean = false

  constructor(oldState: State, newState: string, action: string)
  abort(fsm: IFSM): void
  toString(): string   // returns `${action}ing`
}

Fields

Field	Description
`oldState`	starting state
`newState`	target state (the stable state after success)
`action`	action name (defaults to the decorated method name; overridable via `opt.action`)
`aborted`	whether it has been aborted

toString

const m = new MiddleState('idle', 'done', 'fetch')
m.toString()   // 'fetching'

The state property returns this MiddleState instance during the intermediate phase, but state.toString() always returns the string form.

abort

abort(fsm: IFSM): void

Aborts this intermediate state:

Sets aborted = true
Calls setState.call(fsm, oldState, new Error("action '{action}' aborted"))
State rolls back to oldState; stateChanged event fires (with error)

After abort, if the original method is still running, its success callback checks middle.aborted and skips setState(to) if aborted.

When it appears

Created automatically when a @ChangeState-decorated method is called:

@ChangeState('idle', 'done')
async fetch() {
  // here this.state is MiddleState('idle', 'done', 'fetch')
  // this.state.toString() === 'fetching'
}

Listening to intermediate states

Intermediate states dispatch an event with name ${action}ing:

obj.on('fetching', (oldState) => {
  console.log('fetch started, old state', oldState)
})

They also appear as the newState parameter of the stateChanged event (as a MiddleState instance).