Provide a state machine implementation for use in ImpactJS games through one class, StateMachine.

Sometimes you have to pull out the big guns.

If you have sections of your entity code that are tangles of if-then-else, you might need a state machine. State machines are great for:

• AI. Enemies can get into an aggro state if the player attacks them but should "cool down" after five seconds.
• Animation. The player entity should only play the crouching animation once, and then should show the crouched animation.

Instantiate a state machine:

var sm = new StateMachine();

Add states:

sm.state('foo', {
  update: function() { console.log('foo'); }
});

sm.state('bar', {
  update: function() { console.log('bar'); }
});

Call in update:

sm.update();

state('stateName', {})
state('stateName')

Two forms: first adds a new state by that name to the state machine. Second retrieves the state's definition for that name, if any.

The first state added will be the initialState when the state machine starts running.

{
  enter: function() {},
  update: function() {},
  exit: function()
}

All optional. enter called when state is transitioned to, update on every cycle of the state machine, exit before the state is transitioned out of.

All methods are called within the context of the state machine instance; any properties set on the state machine instance will be available as properties on this within the methods.

transition('transitionName', 'fromStateName', 'toStateName', function() {})
transition('transitionName')

Define a transition between two states with the given name. Retrieve the named transition.

The transition method should return true if the transition should be taken. Transition checking will short-circuit if one transition returns true.

Call this every frame, possibly in an entity's update method.

If this is a new state, then the state's enter function will be called. The update method of the state will be called next. If any of the transitions' predicates return true then the current state's exit method will be called and the new state will be entered on the next call to update.

Copyright (c) 2013-2021 David Hayes

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