Warning: .can will cause a conditional transaction function to be called twice

[Brandon Li]

Do not use .can if you pass a non-pure or non-idempotent function to the to attribute.

The .can function is implemented by invoking the function in the to attribute.

If used, .can would even break the example in the official docs where each to attribute increments the character: https://github.com/jakesgordon/javascript-state-machine/blob/master/docs/states-and-transitions.md#conditional-transitions

  seek: function(transition, args) {
    var wildcard = this.config.defaults.wildcard,
        entry    = this.config.transitionFor(this.state, transition),
        to       = entry && entry.to;
    if (typeof to === 'function')
      return to.apply(this.context, args); // BUG HERE. Replace this code with something like return true;
    else if (to === wildcard)
      return this.state
    else
      return to
  },

from: https://github.com/jakesgordon/javascript-state-machine/blob/0d603577423244228cebcd62e60dbbfff27c6ea3/src/jsm.js#L55C1-L65C5