statechart.js

The statechart module provides a State object that is an implementation of a Harel Statechart.

Statecharts are an improvement over state machines because they elegantly solve the state explosion problem that is common with state machines. They do this by adding two additional features to state machines - state clustering and concurrent states. State clustering provides an abstraction over lower level states where events can be handled and transitions made in one place instead of many. Concurrent states essentially allow multiple statecharts to operate independently. The presence of concurrent states means that the current state of a statechart is actually a vector of states whose length is not fixed.

More information on statecharts is available here:

• http://www.wisdom.weizmann.ac.il/~harel/papers/Statecharts.pdf
• http://www.wisdom.weizmann.ac.il/~harel/papers/Statecharts.History.pdf
• http://www.amazon.com/Constructing-User-Interface-Statecharts-Horrocks/dp/0201342782

Examples

Lockable Door

var State = (typeof require === 'function' ? require('statechart') : window.statechart).State;

var door = State.define(function() {
  this.state('closed', function() {
    this.state('locked', function() {
      this.event('unlockDoor', function() { this.goto('../unlocked'); });
    });

    this.state('unlocked', function() {
      this.event('lockDoor', function() { this.goto('../locked'); });
      this.event('openDoor', function() { this.goto('/opened'); });
    });

    this.event('knock', function() { console.log('*knock knock*'); });
  });

  this.state('opened', function() {
    this.event('closeDoor', function() { this.goto('/closed/unlocked'); });
  });
});

door.goto();
door.current();          // => [ '/closed/locked' ]
door.send('knock');      // *knock knock*
door.current();          // => [ '/closed/locked' ]
door.send('unlockDoor');
door.current();          // => [ '/closed/unlocked' ]
door.send('knock');      // *knock knock*
door.send('openDoor');
door.current();          // => [ '/opened' ]
door.send('closeDoor');
door.current();          // => [ '/closed/unlocked' ]
door.send('lockDoor');
door.current();          // => [ '/closed/locked' ]

Shallow History State

var State = (typeof require === 'function' ? require('statechart') : window.statechart).State;

var sc = State.define(function() {
  // State /a is marked as a history state, so any time /a is entered without
  // specifying which substate to enter, the most recently exited substate of /a
  // is chosen (or the first substate if /a has never been entered).
  this.state('a', {H: true}, function() {
    this.state('a.1')
    this.state('a.2')
    this.state('a.3')
  });

  this.state('b', function() {
    this.state('b.1')
    this.state('b.2')
    this.state('b.3')
  });
});

sc.goto('/a/a.2');
sc.current(); // => ['/a/a.2']

sc.goto('/b');
sc.current(); // => ['/b/b.1']

sc.goto('/a');
sc.current(); // => ['/a/a.2']

Deep History State

var State = (typeof require === 'function' ? require('statechart') : window.statechart).State;

var sc = State.define(function() {
  // State /a has shallow history tracking.
  this.state('a', {H: true}, function() {
    this.state('a.1', function() {
      this.state('a.1.1');
      this.state('a.1.2');
      this.state('a.1.3');
    });

    this.state('a.2', function() {
      this.state('a.2.1');
      this.state('a.2.2');
      this.state('a.2.3');
    });
  });

  // State /b has deep history tracking. This is the same as making each
  // descendant state of /b a history state.
  this.state('b', {H: '*'}, function() {
    this.state('b.1', function() {
      this.state('b.1.1');
      this.state('b.1.2');
      this.state('b.1.3');
    });

    this.state('b.2', function() {
      this.state('b.2.1');
      this.state('b.2.2');
      this.state('b.2.3');
    });
  });
});

sc.goto('/a/a.2/a.2.2');
sc.current();  // => ['/a/a.2/a.2.2']

sc.goto('/b/b.2/b.2.3');
sc.current();  // => ['/b/b.2/b.2.3']

sc.goto('/a');
sc.current();  // => ['/a/a.2/a.2.1']

sc.goto('/b');
sc.current();  // => ['/b/b.2/b.2.3']

State Concurrency

var State = (typeof require === 'function' ? require('statechart') : window.statechart).State;

var word = State.define({concurrent: true}, function() {
  this.state('bold', function() {
    this.state('off', function() {
      this.event('toggleBold', function() { this.goto('../on'); });
    });

    this.state('on', function() {
      this.event('toggleBold', function() { this.goto('../off'); });
    });
  });

  this.state('underline', function() {
    this.state('off', function() {
      this.event('toggleUnderline', function() { this.goto('../on'); });
    });

    this.state('on', function() {
      this.event('toggleUnderline', function() { this.goto('../off'); });
    });
  });

  this.state('align', function() {
    this.state('left');
    this.state('right');
    this.state('center');
    this.state('justify');

    this.event('leftClicked', function() { this.goto('./left');});
    this.event('rightClicked', function() { this.goto('./right');});
    this.event('centerClicked', function() { this.goto('./center');});
    this.event('justifyClicked', function() { this.goto('./justify');});
  });

  this.state('bullets', function() {
    this.state('none', function() {
      this.event('regularClicked', function() { this.goto('../regular'); })
      this.event('numberClicked', function() { this.goto('../number'); })
    });

    this.state('regular', function() {
      this.event('regularClicked', function() { this.goto('../none'); })
      this.event('numberClicked', function() { this.goto('../number'); })
    });

    this.state('number', function() {
      this.event('regularClicked', function() { this.goto('../regular'); })
      this.event('numberClicked', function() { this.goto('../none'); })
    });
  });

  this.event('resetClicked', function() { this.goto(); });
});

word.goto();
word.current(); // => ['/bold/off', '/underline/off', '/align/left', '/bullets/none']

word.send('toggleBold');
word.current(); // => ['/bold/on', '/underline/off', '/align/left', '/bullets/none']

word.send('toggleUnderline');
word.current(); // => ['/bold/on', '/underline/on', '/align/left', '/bullets/none']

word.send('rightClicked');
word.current(); // => ['/bold/on', '/underline/on', '/align/right', '/bullets/none']

word.send('justifyClicked');
word.current(); // => ['/bold/on', '/underline/on', '/align/justify', '/bullets/none']

word.send('regularClicked');
word.current(); // => ['/bold/on', '/underline/on', '/align/justify', '/bullets/regular']

word.send('regularClicked');
word.current(); // => ['/bold/on', '/underline/on', '/align/justify', '/bullets/none']

word.send('numberClicked');
word.current(); // => ['/bold/on', '/underline/on', '/align/justify', '/bullets/number']

word.send('resetClicked');
word.current(); // => ['/bold/off', '/underline/off', '/align/left', '/bullets/none']