Error "transition is invalid in current state" when returning promise from event of type "any"

[beltschatsar]

I get error "​​transition is invalid in current state​​" when using a Promise in following "any" event:

• onBeforeTransition
• onLeaveState
• onTransition

Repro case:

import * as StateMachine from 'javascript-state-machine';

var fsm = new StateMachine({
  init: 'solid',
  transitions: [
        { name: 'melt', from: 'solid', to: 'liquid' },
        { name: 'freeze', from: 'liquid', to: 'solid' },
        { name: 'vaporize', from: 'liquid', to: 'gas' },
        { name: 'condense', from: 'gas', to: 'liquid' }
    ],
    methods: {
        onMelt: function () { console.log('I melted'); return new Promise((resolve, reject) => setTimeout(() => {console.log('onMelt'); resolve(true);}, 1000)); },
        onFreeze: function () { console.log('I froze') },
        onVaporize: function () { console.log('I vaporized') },
        onCondense: function () { console.log('I condensed') },
        onBeforeMelt: function () { return new Promise((resolve, reject) => setTimeout(() => {console.log('onBeforeMelt'); resolve(true);}, 1000)) },
        onLeaveSolid: function () { return new Promise((resolve, reject) => setTimeout(() => {console.log('onLeaveSolid'); resolve(true);}, 1000)) },
        // Following ​​Throws "transition is invalid in current state​​"
        onBeforeTransition: function () { return new Promise((resolve, reject) => setTimeout(() => {console.log('onBeforeTransition'); resolve(true);}, 1000)) },
        onLeaveState: function () { return new Promise((resolve, reject) => setTimeout(() => {console.log('onLeaveState'); resolve(true);}, 1000)) },
        onTransition: function () { return new Promise((resolve, reject) => setTimeout(() => {console.log('onTransition'); resolve(true);}, 1000)) },
    }
});

fsm.melt();

I would expect the output to be:

onBeforeTransition
​​​​​onBeforeMelt​​​​​
onLeaveState
​​​​​onLeaveSolid​​​​​
onTransition
I melted
​​​​​onMelt​​​​​

I got:

​​transition is invalid in current state​​

[NelsonFrancisco]

I would say this happens because:

• You are entering on solid
• So, some method callbacks will be called. Some of which are returning promises that must be resolved before you make the next transition, otherwise you will never leave solid state
  • But you are making a transition fsm.melt() immediately after building a new StateMachine.
  • You never waited for onLeaveSolid or onLeaveState promise to be resolved

As for the solution, I'm not sure. I cannot solve this problem too: When you return a promise in one of the initial state's methods, how do you resolve it?