From 0aca2ddc5982529ce35d0dcc55197dc0af9693f9 Mon Sep 17 00:00:00 2001
From: Nelson Francisco <nelson_cunha1991@hotmail.com>
Date: Fri, 17 May 2019 17:31:21 +0100
Subject: [PATCH 1/8] Transition cancel on state on exception thrown in
 observers

If the state was already mutated, the state goes back.
If it is a promise, then it catches the promise exception, reverts the state, and throws the error again.
---
 src/jsm.js | 27 +++++++++++++++++++++++----
 1 file changed, 23 insertions(+), 4 deletions(-)

diff --git a/src/jsm.js b/src/jsm.js
index f83c8de..060ea5c 100644
--- a/src/jsm.js
+++ b/src/jsm.js
@@ -108,7 +108,13 @@ mixin(JSM.prototype, {
 
   beginTransit: function()          { this.pending = true;                 },
   endTransit:   function(result)    { this.pending = false; return result; },
-  failTransit:  function(result)    { this.pending = false; throw result;  },
+  failTransit:  function(result, from, to) {
+    if (this.state === to) {
+       this.state = from;
+    }
+    this.pending = false;
+    throw result;
+  },
   doTransit:    function(lifecycle) { this.state = lifecycle.to;           },
 
   observe: function(args) {
@@ -132,6 +138,14 @@ mixin(JSM.prototype, {
     return [ event, result, true ]
   },
 
+  callObserver: function(event, observer, args, from, to) {
+    try {
+      return observer[event].apply(observer, args);
+    } catch (error) {
+      this.failTransit.call(this, error, from, to);
+    }
+  },
+
   observeEvents: function(events, args, previousEvent, previousResult) {
     if (events.length === 0) {
       return this.endTransit(previousResult === undefined ? true : previousResult);
@@ -150,11 +164,16 @@ mixin(JSM.prototype, {
       return this.observeEvents(events, args, event, previousResult);
     }
     else {
-      var observer = observers.shift(),
-          result = observer[event].apply(observer, args);
+      var from = args[0].from;
+      var to = args[0].to;
+      var observer = observers.shift();
+      var result = this.callObserver.call(this, event, observer, args, from, to);
       if (result && typeof result.then === 'function') {
+        var jsm = this
         return result.then(this.observeEvents.bind(this, events, args, event))
-                     .catch(this.failTransit.bind(this))
+                     .catch(function (error) {
+                       jsm.failTransit.call(jsm, error, from, to);
+                     });
       }
       else if (result === false) {
         return this.endTransit(false);

From 13fdfcdced4cb9f5604c85bcbedcf1a617b2e578 Mon Sep 17 00:00:00 2001
From: Nelson Francisco <nelson_cunha1991@hotmail.com>
Date: Fri, 17 May 2019 17:36:24 +0100
Subject: [PATCH 2/8] Testing that the state transition is cancelled

when an error is thrown inside an observer
---
 test/errors.js | 55 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 55 insertions(+)

diff --git a/test/errors.js b/test/errors.js
index fb852ca..a639dc8 100644
--- a/test/errors.js
+++ b/test/errors.js
@@ -158,3 +158,58 @@ test('pending transition handler can be customized', t => {
 })
 
 //-------------------------------------------------------------------------------------------------
+
+test('exception thrown in handler cancels state transition', t => {
+
+  var fsm = new StateMachine({
+    transitions: [
+      { name: 'step1', from: 'none', to: 'A' },
+      { name: 'step2', from: 'A',    to: 'B' }
+    ],
+    methods: {
+      onA:function () {
+        throw new Error('Error thrown in observer')
+      }
+    }
+  });
+
+  t.is(fsm.state,        'none')
+  t.is(fsm.can('step1'),  true)
+  t.is(fsm.can('step2'), false)
+  
+  const error = t.throws(() => {
+    fsm.step1();
+  })
+
+  t.is(error.message,    'Error thrown in observer')
+  t.is(fsm.state,       'none')
+
+})
+
+test('exception with promise thrown in handler cancels state transition', async t => {
+
+  var fsm = new StateMachine({
+    transitions: [
+      { name: 'step1', from: 'none', to: 'A' },
+      { name: 'step2', from: 'A',    to: 'B' }
+    ],
+    methods: {
+      onA: async function () {
+        return Promise.reject(new Error('Error thrown in observer'))
+        }
+      }
+  });
+
+  t.is(fsm.state,        'none')
+  t.is(fsm.can('step1'),  true)
+  t.is(fsm.can('step2'), false)
+
+  try{
+    await fsm.step1()
+    t.is('Should fail', 'fail')
+  }catch(error){
+    t.is(error.message,    'Error thrown in observer')
+  }
+
+  t.is(fsm.state,       'none')
+})
\ No newline at end of file

From e564c3a27d711e955cdb5c6c00b1293567f04970 Mon Sep 17 00:00:00 2001
From: Nelson Francisco <nelson_cunha1991@hotmail.com>
Date: Fri, 17 May 2019 17:37:09 +0100
Subject: [PATCH 3/8] Build output files

---
 dist/state-machine.js     | 27 +++++++++++++++++++++++----
 dist/state-machine.min.js |  2 +-
 lib/state-machine.js      | 27 +++++++++++++++++++++++----
 3 files changed, 47 insertions(+), 9 deletions(-)

diff --git a/dist/state-machine.js b/dist/state-machine.js
index b8b9e37..4d09915 100644
--- a/dist/state-machine.js
+++ b/dist/state-machine.js
@@ -465,7 +465,13 @@ mixin(JSM.prototype, {
 
   beginTransit: function()          { this.pending = true;                 },
   endTransit:   function(result)    { this.pending = false; return result; },
-  failTransit:  function(result)    { this.pending = false; throw result;  },
+  failTransit:  function(result, from, to) {
+    if (this.state === to) {
+       this.state = from;
+    }
+    this.pending = false;
+    throw result;
+  },
   doTransit:    function(lifecycle) { this.state = lifecycle.to;           },
 
   observe: function(args) {
@@ -489,6 +495,14 @@ mixin(JSM.prototype, {
     return [ event, result, true ]
   },
 
+  callObserver: function(event, observer, args, from, to) {
+    try {
+      return observer[event].apply(observer, args);
+    } catch (error) {
+      this.failTransit.call(this, error, from, to);
+    }
+  },
+
   observeEvents: function(events, args, previousEvent, previousResult) {
     if (events.length === 0) {
       return this.endTransit(previousResult === undefined ? true : previousResult);
@@ -507,11 +521,16 @@ mixin(JSM.prototype, {
       return this.observeEvents(events, args, event, previousResult);
     }
     else {
-      var observer = observers.shift(),
-          result = observer[event].apply(observer, args);
+      var from = args[0].from;
+      var to = args[0].to;
+      var observer = observers.shift();
+      var result = this.callObserver.call(this, event, observer, args, from, to);
       if (result && typeof result.then === 'function') {
+        var jsm = this
         return result.then(this.observeEvents.bind(this, events, args, event))
-                     .catch(this.failTransit.bind(this))
+                     .catch(function (error) {
+                       jsm.failTransit.call(jsm, error, from, to);
+                     });
       }
       else if (result === false) {
         return this.endTransit(false);
diff --git a/dist/state-machine.min.js b/dist/state-machine.min.js
index b9439bc..39ca513 100644
--- a/dist/state-machine.min.js
+++ b/dist/state-machine.min.js
@@ -1 +1 @@
-!function(t,n){"object"==typeof exports&&"object"==typeof module?module.exports=n():"function"==typeof define&&define.amd?define("StateMachine",[],n):"object"==typeof exports?exports.StateMachine=n():t.StateMachine=n()}(this,function(){return function(t){function n(e){if(i[e])return i[e].exports;var s=i[e]={i:e,l:!1,exports:{}};return t[e].call(s.exports,s,s.exports,n),s.l=!0,s.exports}var i={};return n.m=t,n.c=i,n.i=function(t){return t},n.d=function(t,i,e){n.o(t,i)||Object.defineProperty(t,i,{configurable:!1,enumerable:!0,get:e})},n.n=function(t){var i=t&&t.__esModule?function(){return t.default}:function(){return t};return n.d(i,"a",i),i},n.o=function(t,n){return Object.prototype.hasOwnProperty.call(t,n)},n.p="",n(n.s=5)}([function(t,n,i){"use strict";t.exports=function(t,n){var i,e,s;for(i=1;i<arguments.length;i++){e=arguments[i];for(s in e)e.hasOwnProperty(s)&&(t[s]=e[s])}return t}},function(t,n,i){"use strict";var e=i(0);t.exports={build:function(t,n){var i,s,r,o=n.plugins;for(i=0,s=o.length;i<s;i++)r=o[i],r.methods&&e(t,r.methods),r.properties&&Object.defineProperties(t,r.properties)},hook:function(t,n,i){var e,s,r,o,a=t.config.plugins,f=[t.context];for(i&&(f=f.concat(i)),e=0,s=a.length;e<s;e++)o=a[e],(r=a[e][n])&&r.apply(o,f)}}},function(t,n,i){"use strict";function e(t){if(0===t.length)return t;var n,i,e=t.split(/[_-]/);if(1===e.length&&e[0][0].toLowerCase()===e[0][0])return t;for(i=e[0].toLowerCase(),n=1;n<e.length;n++)i=i+e[n].charAt(0).toUpperCase()+e[n].substring(1).toLowerCase();return i}e.prepended=function(t,n){return n=e(n),t+n[0].toUpperCase()+n.substring(1)},t.exports=e},function(t,n,i){"use strict";function e(t,n){t=t||{},this.options=t,this.defaults=n.defaults,this.states=[],this.transitions=[],this.map={},this.lifecycle=this.configureLifecycle(),this.init=this.configureInitTransition(t.init),this.data=this.configureData(t.data),this.methods=this.configureMethods(t.methods),this.map[this.defaults.wildcard]={},this.configureTransitions(t.transitions||[]),this.plugins=this.configurePlugins(t.plugins,n.plugin)}var s=i(0),r=i(2);s(e.prototype,{addState:function(t){this.map[t]||(this.states.push(t),this.addStateLifecycleNames(t),this.map[t]={})},addStateLifecycleNames:function(t){this.lifecycle.onEnter[t]=r.prepended("onEnter",t),this.lifecycle.onLeave[t]=r.prepended("onLeave",t),this.lifecycle.on[t]=r.prepended("on",t)},addTransition:function(t){this.transitions.indexOf(t)<0&&(this.transitions.push(t),this.addTransitionLifecycleNames(t))},addTransitionLifecycleNames:function(t){this.lifecycle.onBefore[t]=r.prepended("onBefore",t),this.lifecycle.onAfter[t]=r.prepended("onAfter",t),this.lifecycle.on[t]=r.prepended("on",t)},mapTransition:function(t){var n=t.name,i=t.from,e=t.to;return this.addState(i),"function"!=typeof e&&this.addState(e),this.addTransition(n),this.map[i][n]=t,t},configureLifecycle:function(){return{onBefore:{transition:"onBeforeTransition"},onAfter:{transition:"onAfterTransition"},onEnter:{state:"onEnterState"},onLeave:{state:"onLeaveState"},on:{transition:"onTransition"}}},configureInitTransition:function(t){return"string"==typeof t?this.mapTransition(s({},this.defaults.init,{to:t,active:!0})):"object"==typeof t?this.mapTransition(s({},this.defaults.init,t,{active:!0})):(this.addState(this.defaults.init.from),this.defaults.init)},configureData:function(t){return"function"==typeof t?t:"object"==typeof t?function(){return t}:function(){return{}}},configureMethods:function(t){return t||{}},configurePlugins:function(t,n){t=t||[];var i,e,s;for(i=0,e=t.length;i<e;i++)s=t[i],"function"==typeof s&&(t[i]=s=s()),s.configure&&s.configure(this);return t},configureTransitions:function(t){var n,i,e,s,r,o=this.defaults.wildcard;for(i=0;i<t.length;i++)for(e=t[i],s=Array.isArray(e.from)?e.from:[e.from||o],r=e.to||o,n=0;n<s.length;n++)this.mapTransition({name:e.name,from:s[n],to:r})},transitionFor:function(t,n){var i=this.defaults.wildcard;return this.map[t][n]||this.map[i][n]},transitionsFor:function(t){var n=this.defaults.wildcard;return Object.keys(this.map[t]).concat(Object.keys(this.map[n]))},allStates:function(){return this.states},allTransitions:function(){return this.transitions}}),t.exports=e},function(t,n,i){function e(t,n){this.context=t,this.config=n,this.state=n.init.from,this.observers=[t]}var s=i(0),r=i(6),o=i(1),a=[null,[]];s(e.prototype,{init:function(t){if(s(this.context,this.config.data.apply(this.context,t)),o.hook(this,"init"),this.config.init.active)return this.fire(this.config.init.name,[])},is:function(t){return Array.isArray(t)?t.indexOf(this.state)>=0:this.state===t},isPending:function(){return this.pending},can:function(t){return!this.isPending()&&!!this.seek(t)},cannot:function(t){return!this.can(t)},allStates:function(){return this.config.allStates()},allTransitions:function(){return this.config.allTransitions()},transitions:function(){return this.config.transitionsFor(this.state)},seek:function(t,n){var i=this.config.defaults.wildcard,e=this.config.transitionFor(this.state,t),s=e&&e.to;return"function"==typeof s?s.apply(this.context,n):s===i?this.state:s},fire:function(t,n){return this.transit(t,this.state,this.seek(t,n),n)},transit:function(t,n,i,e){var s=this.config.lifecycle,r=this.config.options.observeUnchangedState||n!==i;return i?this.isPending()?this.context.onPendingTransition(t,n,i):(this.config.addState(i),this.beginTransit(),e.unshift({transition:t,from:n,to:i,fsm:this.context}),this.observeEvents([this.observersForEvent(s.onBefore.transition),this.observersForEvent(s.onBefore[t]),r?this.observersForEvent(s.onLeave.state):a,r?this.observersForEvent(s.onLeave[n]):a,this.observersForEvent(s.on.transition),r?["doTransit",[this]]:a,r?this.observersForEvent(s.onEnter.state):a,r?this.observersForEvent(s.onEnter[i]):a,r?this.observersForEvent(s.on[i]):a,this.observersForEvent(s.onAfter.transition),this.observersForEvent(s.onAfter[t]),this.observersForEvent(s.on[t])],e)):this.context.onInvalidTransition(t,n,i)},beginTransit:function(){this.pending=!0},endTransit:function(t){return this.pending=!1,t},failTransit:function(t){throw this.pending=!1,t},doTransit:function(t){this.state=t.to},observe:function(t){if(2===t.length){var n={};n[t[0]]=t[1],this.observers.push(n)}else this.observers.push(t[0])},observersForEvent:function(t){for(var n,i=0,e=this.observers.length,s=[];i<e;i++)n=this.observers[i],n[t]&&s.push(n);return[t,s,!0]},observeEvents:function(t,n,i,e){if(0===t.length)return this.endTransit(void 0===e||e);var s=t[0][0],r=t[0][1],a=t[0][2];if(n[0].event=s,s&&a&&s!==i&&o.hook(this,"lifecycle",n),0===r.length)return t.shift(),this.observeEvents(t,n,s,e);var f=r.shift(),c=f[s].apply(f,n);return c&&"function"==typeof c.then?c.then(this.observeEvents.bind(this,t,n,s)).catch(this.failTransit.bind(this)):!1===c?this.endTransit(!1):this.observeEvents(t,n,s,c)},onInvalidTransition:function(t,n,i){throw new r("transition is invalid in current state",t,n,i,this.state)},onPendingTransition:function(t,n,i){throw new r("transition is invalid while previous transition is still in progress",t,n,i,this.state)}}),t.exports=e},function(t,n,i){"use strict";function e(t){return r(this||{},t)}function s(){var t,n;"function"==typeof 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\ No newline at end of file
+!function(t,n){"object"==typeof exports&&"object"==typeof module?module.exports=n():"function"==typeof define&&define.amd?define("StateMachine",[],n):"object"==typeof exports?exports.StateMachine=n():t.StateMachine=n()}(this,function(){return function(t){function n(e){if(i[e])return i[e].exports;var s=i[e]={i:e,l:!1,exports:{}};return t[e].call(s.exports,s,s.exports,n),s.l=!0,s.exports}var i={};return n.m=t,n.c=i,n.i=function(t){return t},n.d=function(t,i,e){n.o(t,i)||Object.defineProperty(t,i,{configurable:!1,enumerable:!0,get:e})},n.n=function(t){var i=t&&t.__esModule?function(){return t.default}:function(){return t};return n.d(i,"a",i),i},n.o=function(t,n){return Object.prototype.hasOwnProperty.call(t,n)},n.p="",n(n.s=5)}([function(t,n,i){"use strict";t.exports=function(t,n){var i,e,s;for(i=1;i<arguments.length;i++){e=arguments[i];for(s in e)e.hasOwnProperty(s)&&(t[s]=e[s])}return t}},function(t,n,i){"use strict";var e=i(0);t.exports={build:function(t,n){var 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s=i(0),r=i(2);s(e.prototype,{addState:function(t){this.map[t]||(this.states.push(t),this.addStateLifecycleNames(t),this.map[t]={})},addStateLifecycleNames:function(t){this.lifecycle.onEnter[t]=r.prepended("onEnter",t),this.lifecycle.onLeave[t]=r.prepended("onLeave",t),this.lifecycle.on[t]=r.prepended("on",t)},addTransition:function(t){this.transitions.indexOf(t)<0&&(this.transitions.push(t),this.addTransitionLifecycleNames(t))},addTransitionLifecycleNames:function(t){this.lifecycle.onBefore[t]=r.prepended("onBefore",t),this.lifecycle.onAfter[t]=r.prepended("onAfter",t),this.lifecycle.on[t]=r.prepended("on",t)},mapTransition:function(t){var n=t.name,i=t.from,e=t.to;return this.addState(i),"function"!=typeof 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n,i,e,s,r,o=this.defaults.wildcard;for(i=0;i<t.length;i++)for(e=t[i],s=Array.isArray(e.from)?e.from:[e.from||o],r=e.to||o,n=0;n<s.length;n++)this.mapTransition({name:e.name,from:s[n],to:r})},transitionFor:function(t,n){var i=this.defaults.wildcard;return this.map[t][n]||this.map[i][n]},transitionsFor:function(t){var n=this.defaults.wildcard;return Object.keys(this.map[t]).concat(Object.keys(this.map[n]))},allStates:function(){return this.states},allTransitions:function(){return this.transitions}}),t.exports=e},function(t,n,i){function e(t,n){this.context=t,this.config=n,this.state=n.init.from,this.observers=[t]}var s=i(0),r=i(6),o=i(1),a=[null,[]];s(e.prototype,{init:function(t){if(s(this.context,this.config.data.apply(this.context,t)),o.hook(this,"init"),this.config.init.active)return this.fire(this.config.init.name,[])},is:function(t){return Array.isArray(t)?t.indexOf(this.state)>=0:this.state===t},isPending:function(){return this.pending},can:function(t){return!this.isPending()&&!!this.seek(t)},cannot:function(t){return!this.can(t)},allStates:function(){return this.config.allStates()},allTransitions:function(){return this.config.allTransitions()},transitions:function(){return this.config.transitionsFor(this.state)},seek:function(t,n){var i=this.config.defaults.wildcard,e=this.config.transitionFor(this.state,t),s=e&&e.to;return"function"==typeof s?s.apply(this.context,n):s===i?this.state:s},fire:function(t,n){return this.transit(t,this.state,this.seek(t,n),n)},transit:function(t,n,i,e){var s=this.config.lifecycle,r=this.config.options.observeUnchangedState||n!==i;return i?this.isPending()?this.context.onPendingTransition(t,n,i):(this.config.addState(i),this.beginTransit(),e.unshift({transition:t,from:n,to:i,fsm:this.context}),this.observeEvents([this.observersForEvent(s.onBefore.transition),this.observersForEvent(s.onBefore[t]),r?this.observersForEvent(s.onLeave.state):a,r?this.observersForEvent(s.onLeave[n]):a,this.observersForEvent(s.on.transition),r?["doTransit",[this]]:a,r?this.observersForEvent(s.onEnter.state):a,r?this.observersForEvent(s.onEnter[i]):a,r?this.observersForEvent(s.on[i]):a,this.observersForEvent(s.onAfter.transition),this.observersForEvent(s.onAfter[t]),this.observersForEvent(s.on[t])],e)):this.context.onInvalidTransition(t,n,i)},beginTransit:function(){this.pending=!0},endTransit:function(t){return this.pending=!1,t},failTransit:function(t,n,i){throw this.state===i&&(this.state=n),this.pending=!1,t},doTransit:function(t){this.state=t.to},observe:function(t){if(2===t.length){var n={};n[t[0]]=t[1],this.observers.push(n)}else this.observers.push(t[0])},observersForEvent:function(t){for(var n,i=0,e=this.observers.length,s=[];i<e;i++)n=this.observers[i],n[t]&&s.push(n);return[t,s,!0]},callObserver:function(t,n,i,e,s){try{return n[t].apply(n,i)}catch(t){this.failTransit.call(this,t,e,s)}},observeEvents:function(t,n,i,e){if(0===t.length)return this.endTransit(void 0===e||e);var s=t[0][0],r=t[0][1],a=t[0][2];if(n[0].event=s,s&&a&&s!==i&&o.hook(this,"lifecycle",n),0===r.length)return t.shift(),this.observeEvents(t,n,s,e);var f=n[0].from,c=n[0].to,u=r.shift(),h=this.callObserver.call(this,s,u,n,f,c);if(h&&"function"==typeof h.then){var l=this;return h.then(this.observeEvents.bind(this,t,n,s)).catch(function(t){l.failTransit.call(l,t,f,c)})}return!1===h?this.endTransit(!1):this.observeEvents(t,n,s,h)},onInvalidTransition:function(t,n,i){throw new r("transition is invalid in current state",t,n,i,this.state)},onPendingTransition:function(t,n,i){throw new r("transition is invalid while previous transition is still in progress",t,n,i,this.state)}}),t.exports=e},function(t,n,i){"use strict";function e(t){return r(this||{},t)}function s(){var t,n;"function"==typeof arguments[0]?(t=arguments[0],n=arguments[1]||{}):(t=function(){this._fsm.apply(this,arguments)},n=arguments[0]||{});var i=new u(n,e);return o(t.prototype,i),t.prototype._fsm.config=i,t}function r(t,n){return o(t,new u(n,e)),t._fsm(),t}function o(t,n){if("object"!=typeof t||Array.isArray(t))throw Error("StateMachine can only be applied to objects");c.build(t,n),Object.defineProperties(t,p),a(t,l),a(t,n.methods),n.allTransitions().forEach(function(n){t[f(n)]=function(){return this._fsm.fire(n,[].slice.call(arguments))}}),t._fsm=function(){this._fsm=new h(this,n),this._fsm.init(arguments)}}var a=i(0),f=i(2),c=i(1),u=i(3),h=i(4),l={is:function(t){return this._fsm.is(t)},can:function(t){return this._fsm.can(t)},cannot:function(t){return this._fsm.cannot(t)},observe:function(){return this._fsm.observe(arguments)},transitions:function(){return this._fsm.transitions()},allTransitions:function(){return this._fsm.allTransitions()},allStates:function(){return this._fsm.allStates()},onInvalidTransition:function(t,n,i){return this._fsm.onInvalidTransition(t,n,i)},onPendingTransition:function(t,n,i){return this._fsm.onPendingTransition(t,n,i)}},p={state:{configurable:!1,enumerable:!0,get:function(){return this._fsm.state},set:function(t){throw Error("use transitions to change state")}}};e.version="3.0.1",e.factory=s,e.apply=r,e.defaults={wildcard:"*",init:{name:"init",from:"none"}},t.exports=e},function(t,n,i){"use strict";t.exports=function(t,n,i,e,s){this.message=t,this.transition=n,this.from=i,this.to=e,this.current=s}}])});
\ No newline at end of file
diff --git a/lib/state-machine.js b/lib/state-machine.js
index b8b9e37..4d09915 100644
--- a/lib/state-machine.js
+++ b/lib/state-machine.js
@@ -465,7 +465,13 @@ mixin(JSM.prototype, {
 
   beginTransit: function()          { this.pending = true;                 },
   endTransit:   function(result)    { this.pending = false; return result; },
-  failTransit:  function(result)    { this.pending = false; throw result;  },
+  failTransit:  function(result, from, to) {
+    if (this.state === to) {
+       this.state = from;
+    }
+    this.pending = false;
+    throw result;
+  },
   doTransit:    function(lifecycle) { this.state = lifecycle.to;           },
 
   observe: function(args) {
@@ -489,6 +495,14 @@ mixin(JSM.prototype, {
     return [ event, result, true ]
   },
 
+  callObserver: function(event, observer, args, from, to) {
+    try {
+      return observer[event].apply(observer, args);
+    } catch (error) {
+      this.failTransit.call(this, error, from, to);
+    }
+  },
+
   observeEvents: function(events, args, previousEvent, previousResult) {
     if (events.length === 0) {
       return this.endTransit(previousResult === undefined ? true : previousResult);
@@ -507,11 +521,16 @@ mixin(JSM.prototype, {
       return this.observeEvents(events, args, event, previousResult);
     }
     else {
-      var observer = observers.shift(),
-          result = observer[event].apply(observer, args);
+      var from = args[0].from;
+      var to = args[0].to;
+      var observer = observers.shift();
+      var result = this.callObserver.call(this, event, observer, args, from, to);
       if (result && typeof result.then === 'function') {
+        var jsm = this
         return result.then(this.observeEvents.bind(this, events, args, event))
-                     .catch(this.failTransit.bind(this))
+                     .catch(function (error) {
+                       jsm.failTransit.call(jsm, error, from, to);
+                     });
       }
       else if (result === false) {
         return this.endTransit(false);

From ca5ef8653c9506221ac9661895fe30d635aae474 Mon Sep 17 00:00:00 2001
From: Nelson Francisco <nelson_cunha1991@hotmail.com>
Date: Fri, 17 May 2019 17:40:29 +0100
Subject: [PATCH 4/8] Doc update transition cancel

---
 docs/lifecycle-events.md | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/docs/lifecycle-events.md b/docs/lifecycle-events.md
index bb3381b..8add4a3 100644
--- a/docs/lifecycle-events.md
+++ b/docs/lifecycle-events.md
@@ -146,3 +146,6 @@ lifecycle events:
 
 All subsequent lifecycle events will be cancelled and the state will remain unchanged.
 
+To cancel a transition, you can also throw an exception `throw new Error('')` or await for a promise that is rejected inside any lifecycle handler.
+The transition state will be cancelled and the following lifecycle events will not be triggered
+

From 640479942ececa7bbd605430cfa9102537b4962a Mon Sep 17 00:00:00 2001
From: Nelson Francisco <nelson_cunha1991@hotmail.com>
Date: Sat, 18 May 2019 11:40:14 +0100
Subject: [PATCH 5/8] Notify plugins of transition cancelation

---
 src/jsm.js | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/src/jsm.js b/src/jsm.js
index 060ea5c..0985aa1 100644
--- a/src/jsm.js
+++ b/src/jsm.js
@@ -108,9 +108,13 @@ mixin(JSM.prototype, {
 
   beginTransit: function()          { this.pending = true;                 },
   endTransit:   function(result)    { this.pending = false; return result; },
-  failTransit:  function(result, from, to) {
+  failTransit:  function(result, args) {
+    var from = args[0].from;
+    var to = args[0].to;
+
     if (this.state === to) {
-       this.state = from;
+      this.state = from;
+      plugin.hook(this, 'cancel', args);
     }
     this.pending = false;
     throw result;
@@ -138,11 +142,11 @@ mixin(JSM.prototype, {
     return [ event, result, true ]
   },
 
-  callObserver: function(event, observer, args, from, to) {
+  callObserver: function(event, observer, args) {
     try {
       return observer[event].apply(observer, args);
     } catch (error) {
-      this.failTransit.call(this, error, from, to);
+      this.failTransit.call(this, error, args);
     }
   },
 
@@ -164,15 +168,13 @@ mixin(JSM.prototype, {
       return this.observeEvents(events, args, event, previousResult);
     }
     else {
-      var from = args[0].from;
-      var to = args[0].to;
       var observer = observers.shift();
-      var result = this.callObserver.call(this, event, observer, args, from, to);
+      var result = this.callObserver.call(this, event, observer, args);
       if (result && typeof result.then === 'function') {
         var jsm = this
         return result.then(this.observeEvents.bind(this, events, args, event))
                      .catch(function (error) {
-                       jsm.failTransit.call(jsm, error, from, to);
+                       jsm.failTransit.call(jsm, error, args);
                      });
       }
       else if (result === false) {

From 0d181d17ac42d9a662eef369e32db570cff029ba Mon Sep 17 00:00:00 2001
From: Nelson Francisco <nelson_cunha1991@hotmail.com>
Date: Sat, 18 May 2019 11:42:45 +0100
Subject: [PATCH 6/8] History plugin - cancel pop one state

---
 src/plugin/history.js | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/plugin/history.js b/src/plugin/history.js
index 46799c0..8b7e67d 100644
--- a/src/plugin/history.js
+++ b/src/plugin/history.js
@@ -39,6 +39,10 @@ module.exports = function(options) { options = options || {};
       }
     },
 
+    cancel: function(instance, lifecycle) {
+      instance[past].pop()
+    },
+
     methods:    {},
     properties: {}
 

From f992077de97c79387efd23cbb4475a379b7b04f5 Mon Sep 17 00:00:00 2001
From: Nelson Francisco <nelson_cunha1991@hotmail.com>
Date: Sat, 18 May 2019 11:43:09 +0100
Subject: [PATCH 7/8] History plugin test transition cancel

---
 test/plugin/history.js | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/test/plugin/history.js b/test/plugin/history.js
index 00f73ef..bfbdd5d 100644
--- a/test/plugin/history.js
+++ b/test/plugin/history.js
@@ -491,3 +491,35 @@ test('history can be used with a state machine factory applied to existing class
 })
 
 //-------------------------------------------------------------------------------------------------
+
+test('exception thrown in handler cancels state transition', t => {
+
+  var fsm = new StateMachine({
+    transitions: [
+      { name: 'step1', from: 'none', to: 'A' },
+      { name: 'step2', from: 'A',    to: 'B' }
+    ],
+    plugins:[
+      StateMachineHistory
+    ],
+    methods: {
+      onB:function () {
+        throw new Error('Error thrown in observer')
+      }
+    }
+  });
+
+  t.is(fsm.state,        'none'); t.deepEqual(fsm.history, [ ]);
+  t.is(fsm.can('step1'),  true)
+  t.is(fsm.can('step2'), false)
+
+  fsm.step1();  t.is(fsm.state,        'A'); t.deepEqual(fsm.history, [ 'A' ]);
+  
+  const error = t.throws(() => {
+    fsm.step2();
+  })
+
+  t.is(fsm.state,        'A'); t.deepEqual(fsm.history, [ 'A' ]);
+
+  t.is(error.message,    'Error thrown in observer')
+})
\ No newline at end of file

From a72fa564b268c9092584d287c0695148e8c6495f Mon Sep 17 00:00:00 2001
From: Nelson Francisco <nelson_cunha1991@hotmail.com>
Date: Sat, 18 May 2019 12:07:47 +0100
Subject: [PATCH 8/8] Build output files

---
 dist/state-machine-history.js     |  4 ++++
 dist/state-machine-history.min.js |  2 +-
 dist/state-machine.js             | 18 ++++++++++--------
 dist/state-machine.min.js         |  2 +-
 lib/history.js                    |  4 ++++
 lib/state-machine.js              | 18 ++++++++++--------
 6 files changed, 30 insertions(+), 18 deletions(-)

diff --git a/dist/state-machine-history.js b/dist/state-machine-history.js
index 19f7c4f..cd50b65 100644
--- a/dist/state-machine-history.js
+++ b/dist/state-machine-history.js
@@ -162,6 +162,10 @@ module.exports = function(options) { options = options || {};
       }
     },
 
+    cancel: function(instance, lifecycle) {
+      instance[past].pop()
+    },
+
     methods:    {},
     properties: {}
 
diff --git a/dist/state-machine-history.min.js b/dist/state-machine-history.min.js
index 9c7fb3f..b5e601a 100644
--- a/dist/state-machine-history.min.js
+++ b/dist/state-machine-history.min.js
@@ -1 +1 @@
-!function(t,e){"object"==typeof exports&&"object"==typeof module?module.exports=e():"function"==typeof define&&define.amd?define("StateMachineHistory",[],e):"object"==typeof exports?exports.StateMachineHistory=e():t.StateMachineHistory=e()}(this,function(){return function(t){function e(r){if(n[r])return n[r].exports;var o=n[r]={i:r,l:!1,exports:{}};return t[r].call(o.exports,o,o.exports,e),o.l=!0,o.exports}var n={};return e.m=t,e.c=n,e.i=function(t){return t},e.d=function(t,n,r){e.o(t,n)||Object.defineProperty(t,n,{configurable:!1,enumerable:!0,get:r})},e.n=function(t){var n=t&&t.__esModule?function(){return t.default}:function(){return t};return e.d(n,"a",n),n},e.o=function(t,e){return Object.prototype.hasOwnProperty.call(t,e)},e.p="",e(e.s=1)}([function(t,e,n){"use strict";function r(t){if(0===t.length)return t;var e,n,r=t.split(/[_-]/);if(1===r.length&&r[0][0].toLowerCase()===r[0][0])return t;for(n=r[0].toLowerCase(),e=1;e<r.length;e++)n=n+r[e].charAt(0).toUpperCase()+r[e].substring(1).toLowerCase();return n}r.prepended=function(t,e){return e=r(e),t+e[0].toUpperCase()+e.substring(1)},t.exports=r},function(t,e,n){"use strict";var r=n(0);t.exports=function(t){t=t||{};var e=r(t.name||t.past||"history"),n=r(t.future||"future"),o=r.prepended("clear",e),i=r.prepended(e,"back"),s=r.prepended(e,"forward"),u=r.prepended("can",i),p=r.prepended("can",s),c=t.max,f={configure:function(t){t.addTransitionLifecycleNames(i),t.addTransitionLifecycleNames(s)},init:function(t){t[e]=[],t[n]=[]},lifecycle:function(t,r){"onEnterState"===r.event&&(t[e].push(r.to),c&&t[e].length>c&&t[e].shift(),r.transition!==i&&r.transition!==s&&(t[n].length=0))},methods:{},properties:{}};return f.methods[o]=function(){this[e].length=0,this[n].length=0},f.properties[u]={get:function(){return this[e].length>1}},f.properties[p]={get:function(){return this[n].length>0}},f.methods[i]=function(){if(!this[u])throw Error("no history");var t=this[e].pop(),r=this[e].pop();this[n].push(t),this._fsm.transit(i,t,r,[])},f.methods[s]=function(){if(!this[p])throw Error("no history");var t=this.state,e=this[n].pop();this._fsm.transit(s,t,e,[])},f}}])});
\ No newline at end of file
+!function(t,e){"object"==typeof exports&&"object"==typeof module?module.exports=e():"function"==typeof define&&define.amd?define("StateMachineHistory",[],e):"object"==typeof exports?exports.StateMachineHistory=e():t.StateMachineHistory=e()}(this,function(){return function(t){function e(r){if(n[r])return n[r].exports;var o=n[r]={i:r,l:!1,exports:{}};return t[r].call(o.exports,o,o.exports,e),o.l=!0,o.exports}var n={};return e.m=t,e.c=n,e.i=function(t){return t},e.d=function(t,n,r){e.o(t,n)||Object.defineProperty(t,n,{configurable:!1,enumerable:!0,get:r})},e.n=function(t){var n=t&&t.__esModule?function(){return t.default}:function(){return t};return e.d(n,"a",n),n},e.o=function(t,e){return Object.prototype.hasOwnProperty.call(t,e)},e.p="",e(e.s=1)}([function(t,e,n){"use strict";function r(t){if(0===t.length)return t;var e,n,r=t.split(/[_-]/);if(1===r.length&&r[0][0].toLowerCase()===r[0][0])return t;for(n=r[0].toLowerCase(),e=1;e<r.length;e++)n=n+r[e].charAt(0).toUpperCase()+r[e].substring(1).toLowerCase();return n}r.prepended=function(t,e){return e=r(e),t+e[0].toUpperCase()+e.substring(1)},t.exports=r},function(t,e,n){"use strict";var r=n(0);t.exports=function(t){t=t||{};var e=r(t.name||t.past||"history"),n=r(t.future||"future"),o=r.prepended("clear",e),i=r.prepended(e,"back"),s=r.prepended(e,"forward"),u=r.prepended("can",i),p=r.prepended("can",s),c=t.max,f={configure:function(t){t.addTransitionLifecycleNames(i),t.addTransitionLifecycleNames(s)},init:function(t){t[e]=[],t[n]=[]},lifecycle:function(t,r){"onEnterState"===r.event&&(t[e].push(r.to),c&&t[e].length>c&&t[e].shift(),r.transition!==i&&r.transition!==s&&(t[n].length=0))},cancel:function(t,n){t[e].pop()},methods:{},properties:{}};return f.methods[o]=function(){this[e].length=0,this[n].length=0},f.properties[u]={get:function(){return this[e].length>1}},f.properties[p]={get:function(){return this[n].length>0}},f.methods[i]=function(){if(!this[u])throw Error("no history");var t=this[e].pop(),r=this[e].pop();this[n].push(t),this._fsm.transit(i,t,r,[])},f.methods[s]=function(){if(!this[p])throw Error("no history");var t=this.state,e=this[n].pop();this._fsm.transit(s,t,e,[])},f}}])});
\ No newline at end of file
diff --git a/dist/state-machine.js b/dist/state-machine.js
index 4d09915..3177183 100644
--- a/dist/state-machine.js
+++ b/dist/state-machine.js
@@ -465,9 +465,13 @@ mixin(JSM.prototype, {
 
   beginTransit: function()          { this.pending = true;                 },
   endTransit:   function(result)    { this.pending = false; return result; },
-  failTransit:  function(result, from, to) {
+  failTransit:  function(result, args) {
+    var from = args[0].from;
+    var to = args[0].to;
+
     if (this.state === to) {
-       this.state = from;
+      this.state = from;
+      plugin.hook(this, 'cancel', args);
     }
     this.pending = false;
     throw result;
@@ -495,11 +499,11 @@ mixin(JSM.prototype, {
     return [ event, result, true ]
   },
 
-  callObserver: function(event, observer, args, from, to) {
+  callObserver: function(event, observer, args) {
     try {
       return observer[event].apply(observer, args);
     } catch (error) {
-      this.failTransit.call(this, error, from, to);
+      this.failTransit.call(this, error, args);
     }
   },
 
@@ -521,15 +525,13 @@ mixin(JSM.prototype, {
       return this.observeEvents(events, args, event, previousResult);
     }
     else {
-      var from = args[0].from;
-      var to = args[0].to;
       var observer = observers.shift();
-      var result = this.callObserver.call(this, event, observer, args, from, to);
+      var result = this.callObserver.call(this, event, observer, args);
       if (result && typeof result.then === 'function') {
         var jsm = this
         return result.then(this.observeEvents.bind(this, events, args, event))
                      .catch(function (error) {
-                       jsm.failTransit.call(jsm, error, from, to);
+                       jsm.failTransit.call(jsm, error, args);
                      });
       }
       else if (result === false) {
diff --git a/dist/state-machine.min.js b/dist/state-machine.min.js
index 39ca513..fc361d5 100644
--- a/dist/state-machine.min.js
+++ b/dist/state-machine.min.js
@@ -1 +1 @@
-!function(t,n){"object"==typeof exports&&"object"==typeof module?module.exports=n():"function"==typeof define&&define.amd?define("StateMachine",[],n):"object"==typeof exports?exports.StateMachine=n():t.StateMachine=n()}(this,function(){return function(t){function n(e){if(i[e])return i[e].exports;var s=i[e]={i:e,l:!1,exports:{}};return t[e].call(s.exports,s,s.exports,n),s.l=!0,s.exports}var i={};return n.m=t,n.c=i,n.i=function(t){return t},n.d=function(t,i,e){n.o(t,i)||Object.defineProperty(t,i,{configurable:!1,enumerable:!0,get:e})},n.n=function(t){var i=t&&t.__esModule?function(){return t.default}:function(){return t};return n.d(i,"a",i),i},n.o=function(t,n){return Object.prototype.hasOwnProperty.call(t,n)},n.p="",n(n.s=5)}([function(t,n,i){"use strict";t.exports=function(t,n){var i,e,s;for(i=1;i<arguments.length;i++){e=arguments[i];for(s in e)e.hasOwnProperty(s)&&(t[s]=e[s])}return t}},function(t,n,i){"use strict";var e=i(0);t.exports={build:function(t,n){var i,s,r,o=n.plugins;for(i=0,s=o.length;i<s;i++)r=o[i],r.methods&&e(t,r.methods),r.properties&&Object.defineProperties(t,r.properties)},hook:function(t,n,i){var e,s,r,o,a=t.config.plugins,f=[t.context];for(i&&(f=f.concat(i)),e=0,s=a.length;e<s;e++)o=a[e],(r=a[e][n])&&r.apply(o,f)}}},function(t,n,i){"use strict";function e(t){if(0===t.length)return t;var n,i,e=t.split(/[_-]/);if(1===e.length&&e[0][0].toLowerCase()===e[0][0])return t;for(i=e[0].toLowerCase(),n=1;n<e.length;n++)i=i+e[n].charAt(0).toUpperCase()+e[n].substring(1).toLowerCase();return i}e.prepended=function(t,n){return n=e(n),t+n[0].toUpperCase()+n.substring(1)},t.exports=e},function(t,n,i){"use strict";function e(t,n){t=t||{},this.options=t,this.defaults=n.defaults,this.states=[],this.transitions=[],this.map={},this.lifecycle=this.configureLifecycle(),this.init=this.configureInitTransition(t.init),this.data=this.configureData(t.data),this.methods=this.configureMethods(t.methods),this.map[this.defaults.wildcard]={},this.configureTransitions(t.transitions||[]),this.plugins=this.configurePlugins(t.plugins,n.plugin)}var s=i(0),r=i(2);s(e.prototype,{addState:function(t){this.map[t]||(this.states.push(t),this.addStateLifecycleNames(t),this.map[t]={})},addStateLifecycleNames:function(t){this.lifecycle.onEnter[t]=r.prepended("onEnter",t),this.lifecycle.onLeave[t]=r.prepended("onLeave",t),this.lifecycle.on[t]=r.prepended("on",t)},addTransition:function(t){this.transitions.indexOf(t)<0&&(this.transitions.push(t),this.addTransitionLifecycleNames(t))},addTransitionLifecycleNames:function(t){this.lifecycle.onBefore[t]=r.prepended("onBefore",t),this.lifecycle.onAfter[t]=r.prepended("onAfter",t),this.lifecycle.on[t]=r.prepended("on",t)},mapTransition:function(t){var n=t.name,i=t.from,e=t.to;return this.addState(i),"function"!=typeof e&&this.addState(e),this.addTransition(n),this.map[i][n]=t,t},configureLifecycle:function(){return{onBefore:{transition:"onBeforeTransition"},onAfter:{transition:"onAfterTransition"},onEnter:{state:"onEnterState"},onLeave:{state:"onLeaveState"},on:{transition:"onTransition"}}},configureInitTransition:function(t){return"string"==typeof t?this.mapTransition(s({},this.defaults.init,{to:t,active:!0})):"object"==typeof t?this.mapTransition(s({},this.defaults.init,t,{active:!0})):(this.addState(this.defaults.init.from),this.defaults.init)},configureData:function(t){return"function"==typeof t?t:"object"==typeof t?function(){return t}:function(){return{}}},configureMethods:function(t){return t||{}},configurePlugins:function(t,n){t=t||[];var i,e,s;for(i=0,e=t.length;i<e;i++)s=t[i],"function"==typeof s&&(t[i]=s=s()),s.configure&&s.configure(this);return t},configureTransitions:function(t){var n,i,e,s,r,o=this.defaults.wildcard;for(i=0;i<t.length;i++)for(e=t[i],s=Array.isArray(e.from)?e.from:[e.from||o],r=e.to||o,n=0;n<s.length;n++)this.mapTransition({name:e.name,from:s[n],to:r})},transitionFor:function(t,n){var i=this.defaults.wildcard;return this.map[t][n]||this.map[i][n]},transitionsFor:function(t){var n=this.defaults.wildcard;return Object.keys(this.map[t]).concat(Object.keys(this.map[n]))},allStates:function(){return this.states},allTransitions:function(){return this.transitions}}),t.exports=e},function(t,n,i){function e(t,n){this.context=t,this.config=n,this.state=n.init.from,this.observers=[t]}var s=i(0),r=i(6),o=i(1),a=[null,[]];s(e.prototype,{init:function(t){if(s(this.context,this.config.data.apply(this.context,t)),o.hook(this,"init"),this.config.init.active)return this.fire(this.config.init.name,[])},is:function(t){return Array.isArray(t)?t.indexOf(this.state)>=0:this.state===t},isPending:function(){return this.pending},can:function(t){return!this.isPending()&&!!this.seek(t)},cannot:function(t){return!this.can(t)},allStates:function(){return this.config.allStates()},allTransitions:function(){return this.config.allTransitions()},transitions:function(){return this.config.transitionsFor(this.state)},seek:function(t,n){var i=this.config.defaults.wildcard,e=this.config.transitionFor(this.state,t),s=e&&e.to;return"function"==typeof s?s.apply(this.context,n):s===i?this.state:s},fire:function(t,n){return this.transit(t,this.state,this.seek(t,n),n)},transit:function(t,n,i,e){var s=this.config.lifecycle,r=this.config.options.observeUnchangedState||n!==i;return i?this.isPending()?this.context.onPendingTransition(t,n,i):(this.config.addState(i),this.beginTransit(),e.unshift({transition:t,from:n,to:i,fsm:this.context}),this.observeEvents([this.observersForEvent(s.onBefore.transition),this.observersForEvent(s.onBefore[t]),r?this.observersForEvent(s.onLeave.state):a,r?this.observersForEvent(s.onLeave[n]):a,this.observersForEvent(s.on.transition),r?["doTransit",[this]]:a,r?this.observersForEvent(s.onEnter.state):a,r?this.observersForEvent(s.onEnter[i]):a,r?this.observersForEvent(s.on[i]):a,this.observersForEvent(s.onAfter.transition),this.observersForEvent(s.onAfter[t]),this.observersForEvent(s.on[t])],e)):this.context.onInvalidTransition(t,n,i)},beginTransit:function(){this.pending=!0},endTransit:function(t){return this.pending=!1,t},failTransit:function(t,n,i){throw this.state===i&&(this.state=n),this.pending=!1,t},doTransit:function(t){this.state=t.to},observe:function(t){if(2===t.length){var n={};n[t[0]]=t[1],this.observers.push(n)}else this.observers.push(t[0])},observersForEvent:function(t){for(var n,i=0,e=this.observers.length,s=[];i<e;i++)n=this.observers[i],n[t]&&s.push(n);return[t,s,!0]},callObserver:function(t,n,i,e,s){try{return n[t].apply(n,i)}catch(t){this.failTransit.call(this,t,e,s)}},observeEvents:function(t,n,i,e){if(0===t.length)return this.endTransit(void 0===e||e);var s=t[0][0],r=t[0][1],a=t[0][2];if(n[0].event=s,s&&a&&s!==i&&o.hook(this,"lifecycle",n),0===r.length)return t.shift(),this.observeEvents(t,n,s,e);var f=n[0].from,c=n[0].to,u=r.shift(),h=this.callObserver.call(this,s,u,n,f,c);if(h&&"function"==typeof h.then){var l=this;return h.then(this.observeEvents.bind(this,t,n,s)).catch(function(t){l.failTransit.call(l,t,f,c)})}return!1===h?this.endTransit(!1):this.observeEvents(t,n,s,h)},onInvalidTransition:function(t,n,i){throw new r("transition is invalid in current state",t,n,i,this.state)},onPendingTransition:function(t,n,i){throw new r("transition is invalid while previous transition is still in progress",t,n,i,this.state)}}),t.exports=e},function(t,n,i){"use strict";function e(t){return r(this||{},t)}function s(){var t,n;"function"==typeof arguments[0]?(t=arguments[0],n=arguments[1]||{}):(t=function(){this._fsm.apply(this,arguments)},n=arguments[0]||{});var i=new u(n,e);return o(t.prototype,i),t.prototype._fsm.config=i,t}function r(t,n){return o(t,new u(n,e)),t._fsm(),t}function o(t,n){if("object"!=typeof t||Array.isArray(t))throw Error("StateMachine can only be applied to objects");c.build(t,n),Object.defineProperties(t,p),a(t,l),a(t,n.methods),n.allTransitions().forEach(function(n){t[f(n)]=function(){return this._fsm.fire(n,[].slice.call(arguments))}}),t._fsm=function(){this._fsm=new h(this,n),this._fsm.init(arguments)}}var a=i(0),f=i(2),c=i(1),u=i(3),h=i(4),l={is:function(t){return this._fsm.is(t)},can:function(t){return this._fsm.can(t)},cannot:function(t){return this._fsm.cannot(t)},observe:function(){return this._fsm.observe(arguments)},transitions:function(){return this._fsm.transitions()},allTransitions:function(){return this._fsm.allTransitions()},allStates:function(){return this._fsm.allStates()},onInvalidTransition:function(t,n,i){return this._fsm.onInvalidTransition(t,n,i)},onPendingTransition:function(t,n,i){return this._fsm.onPendingTransition(t,n,i)}},p={state:{configurable:!1,enumerable:!0,get:function(){return this._fsm.state},set:function(t){throw Error("use transitions to change state")}}};e.version="3.0.1",e.factory=s,e.apply=r,e.defaults={wildcard:"*",init:{name:"init",from:"none"}},t.exports=e},function(t,n,i){"use strict";t.exports=function(t,n,i,e,s){this.message=t,this.transition=n,this.from=i,this.to=e,this.current=s}}])});
\ No newline at end of file
+!function(t,n){"object"==typeof exports&&"object"==typeof module?module.exports=n():"function"==typeof define&&define.amd?define("StateMachine",[],n):"object"==typeof exports?exports.StateMachine=n():t.StateMachine=n()}(this,function(){return function(t){function n(e){if(i[e])return i[e].exports;var s=i[e]={i:e,l:!1,exports:{}};return t[e].call(s.exports,s,s.exports,n),s.l=!0,s.exports}var i={};return n.m=t,n.c=i,n.i=function(t){return t},n.d=function(t,i,e){n.o(t,i)||Object.defineProperty(t,i,{configurable:!1,enumerable:!0,get:e})},n.n=function(t){var i=t&&t.__esModule?function(){return t.default}:function(){return t};return n.d(i,"a",i),i},n.o=function(t,n){return Object.prototype.hasOwnProperty.call(t,n)},n.p="",n(n.s=5)}([function(t,n,i){"use strict";t.exports=function(t,n){var i,e,s;for(i=1;i<arguments.length;i++){e=arguments[i];for(s in e)e.hasOwnProperty(s)&&(t[s]=e[s])}return t}},function(t,n,i){"use strict";var e=i(0);t.exports={build:function(t,n){var i,s,r,o=n.plugins;for(i=0,s=o.length;i<s;i++)r=o[i],r.methods&&e(t,r.methods),r.properties&&Object.defineProperties(t,r.properties)},hook:function(t,n,i){var e,s,r,o,a=t.config.plugins,f=[t.context];for(i&&(f=f.concat(i)),e=0,s=a.length;e<s;e++)o=a[e],(r=a[e][n])&&r.apply(o,f)}}},function(t,n,i){"use strict";function e(t){if(0===t.length)return t;var n,i,e=t.split(/[_-]/);if(1===e.length&&e[0][0].toLowerCase()===e[0][0])return t;for(i=e[0].toLowerCase(),n=1;n<e.length;n++)i=i+e[n].charAt(0).toUpperCase()+e[n].substring(1).toLowerCase();return i}e.prepended=function(t,n){return n=e(n),t+n[0].toUpperCase()+n.substring(1)},t.exports=e},function(t,n,i){"use strict";function e(t,n){t=t||{},this.options=t,this.defaults=n.defaults,this.states=[],this.transitions=[],this.map={},this.lifecycle=this.configureLifecycle(),this.init=this.configureInitTransition(t.init),this.data=this.configureData(t.data),this.methods=this.configureMethods(t.methods),this.map[this.defaults.wildcard]={},this.configureTransitions(t.transitions||[]),this.plugins=this.configurePlugins(t.plugins,n.plugin)}var s=i(0),r=i(2);s(e.prototype,{addState:function(t){this.map[t]||(this.states.push(t),this.addStateLifecycleNames(t),this.map[t]={})},addStateLifecycleNames:function(t){this.lifecycle.onEnter[t]=r.prepended("onEnter",t),this.lifecycle.onLeave[t]=r.prepended("onLeave",t),this.lifecycle.on[t]=r.prepended("on",t)},addTransition:function(t){this.transitions.indexOf(t)<0&&(this.transitions.push(t),this.addTransitionLifecycleNames(t))},addTransitionLifecycleNames:function(t){this.lifecycle.onBefore[t]=r.prepended("onBefore",t),this.lifecycle.onAfter[t]=r.prepended("onAfter",t),this.lifecycle.on[t]=r.prepended("on",t)},mapTransition:function(t){var n=t.name,i=t.from,e=t.to;return this.addState(i),"function"!=typeof e&&this.addState(e),this.addTransition(n),this.map[i][n]=t,t},configureLifecycle:function(){return{onBefore:{transition:"onBeforeTransition"},onAfter:{transition:"onAfterTransition"},onEnter:{state:"onEnterState"},onLeave:{state:"onLeaveState"},on:{transition:"onTransition"}}},configureInitTransition:function(t){return"string"==typeof t?this.mapTransition(s({},this.defaults.init,{to:t,active:!0})):"object"==typeof t?this.mapTransition(s({},this.defaults.init,t,{active:!0})):(this.addState(this.defaults.init.from),this.defaults.init)},configureData:function(t){return"function"==typeof t?t:"object"==typeof t?function(){return t}:function(){return{}}},configureMethods:function(t){return t||{}},configurePlugins:function(t,n){t=t||[];var i,e,s;for(i=0,e=t.length;i<e;i++)s=t[i],"function"==typeof s&&(t[i]=s=s()),s.configure&&s.configure(this);return t},configureTransitions:function(t){var n,i,e,s,r,o=this.defaults.wildcard;for(i=0;i<t.length;i++)for(e=t[i],s=Array.isArray(e.from)?e.from:[e.from||o],r=e.to||o,n=0;n<s.length;n++)this.mapTransition({name:e.name,from:s[n],to:r})},transitionFor:function(t,n){var i=this.defaults.wildcard;return this.map[t][n]||this.map[i][n]},transitionsFor:function(t){var n=this.defaults.wildcard;return Object.keys(this.map[t]).concat(Object.keys(this.map[n]))},allStates:function(){return this.states},allTransitions:function(){return this.transitions}}),t.exports=e},function(t,n,i){function e(t,n){this.context=t,this.config=n,this.state=n.init.from,this.observers=[t]}var s=i(0),r=i(6),o=i(1),a=[null,[]];s(e.prototype,{init:function(t){if(s(this.context,this.config.data.apply(this.context,t)),o.hook(this,"init"),this.config.init.active)return this.fire(this.config.init.name,[])},is:function(t){return Array.isArray(t)?t.indexOf(this.state)>=0:this.state===t},isPending:function(){return this.pending},can:function(t){return!this.isPending()&&!!this.seek(t)},cannot:function(t){return!this.can(t)},allStates:function(){return this.config.allStates()},allTransitions:function(){return this.config.allTransitions()},transitions:function(){return this.config.transitionsFor(this.state)},seek:function(t,n){var i=this.config.defaults.wildcard,e=this.config.transitionFor(this.state,t),s=e&&e.to;return"function"==typeof s?s.apply(this.context,n):s===i?this.state:s},fire:function(t,n){return this.transit(t,this.state,this.seek(t,n),n)},transit:function(t,n,i,e){var s=this.config.lifecycle,r=this.config.options.observeUnchangedState||n!==i;return i?this.isPending()?this.context.onPendingTransition(t,n,i):(this.config.addState(i),this.beginTransit(),e.unshift({transition:t,from:n,to:i,fsm:this.context}),this.observeEvents([this.observersForEvent(s.onBefore.transition),this.observersForEvent(s.onBefore[t]),r?this.observersForEvent(s.onLeave.state):a,r?this.observersForEvent(s.onLeave[n]):a,this.observersForEvent(s.on.transition),r?["doTransit",[this]]:a,r?this.observersForEvent(s.onEnter.state):a,r?this.observersForEvent(s.onEnter[i]):a,r?this.observersForEvent(s.on[i]):a,this.observersForEvent(s.onAfter.transition),this.observersForEvent(s.onAfter[t]),this.observersForEvent(s.on[t])],e)):this.context.onInvalidTransition(t,n,i)},beginTransit:function(){this.pending=!0},endTransit:function(t){return this.pending=!1,t},failTransit:function(t,n){var i=n[0].from,e=n[0].to;throw this.state===e&&(this.state=i,o.hook(this,"cancel",n)),this.pending=!1,t},doTransit:function(t){this.state=t.to},observe:function(t){if(2===t.length){var n={};n[t[0]]=t[1],this.observers.push(n)}else this.observers.push(t[0])},observersForEvent:function(t){for(var n,i=0,e=this.observers.length,s=[];i<e;i++)n=this.observers[i],n[t]&&s.push(n);return[t,s,!0]},callObserver:function(t,n,i){try{return n[t].apply(n,i)}catch(t){this.failTransit.call(this,t,i)}},observeEvents:function(t,n,i,e){if(0===t.length)return this.endTransit(void 0===e||e);var s=t[0][0],r=t[0][1],a=t[0][2];if(n[0].event=s,s&&a&&s!==i&&o.hook(this,"lifecycle",n),0===r.length)return t.shift(),this.observeEvents(t,n,s,e);var f=r.shift(),c=this.callObserver.call(this,s,f,n);if(c&&"function"==typeof c.then){var u=this;return c.then(this.observeEvents.bind(this,t,n,s)).catch(function(t){u.failTransit.call(u,t,n)})}return!1===c?this.endTransit(!1):this.observeEvents(t,n,s,c)},onInvalidTransition:function(t,n,i){throw new r("transition is invalid in current state",t,n,i,this.state)},onPendingTransition:function(t,n,i){throw new r("transition is invalid while previous transition is still in progress",t,n,i,this.state)}}),t.exports=e},function(t,n,i){"use strict";function e(t){return r(this||{},t)}function s(){var t,n;"function"==typeof arguments[0]?(t=arguments[0],n=arguments[1]||{}):(t=function(){this._fsm.apply(this,arguments)},n=arguments[0]||{});var i=new u(n,e);return o(t.prototype,i),t.prototype._fsm.config=i,t}function r(t,n){return o(t,new u(n,e)),t._fsm(),t}function o(t,n){if("object"!=typeof t||Array.isArray(t))throw Error("StateMachine can only be applied to objects");c.build(t,n),Object.defineProperties(t,p),a(t,l),a(t,n.methods),n.allTransitions().forEach(function(n){t[f(n)]=function(){return this._fsm.fire(n,[].slice.call(arguments))}}),t._fsm=function(){this._fsm=new h(this,n),this._fsm.init(arguments)}}var a=i(0),f=i(2),c=i(1),u=i(3),h=i(4),l={is:function(t){return this._fsm.is(t)},can:function(t){return this._fsm.can(t)},cannot:function(t){return this._fsm.cannot(t)},observe:function(){return this._fsm.observe(arguments)},transitions:function(){return this._fsm.transitions()},allTransitions:function(){return this._fsm.allTransitions()},allStates:function(){return this._fsm.allStates()},onInvalidTransition:function(t,n,i){return this._fsm.onInvalidTransition(t,n,i)},onPendingTransition:function(t,n,i){return this._fsm.onPendingTransition(t,n,i)}},p={state:{configurable:!1,enumerable:!0,get:function(){return this._fsm.state},set:function(t){throw Error("use transitions to change state")}}};e.version="3.0.1",e.factory=s,e.apply=r,e.defaults={wildcard:"*",init:{name:"init",from:"none"}},t.exports=e},function(t,n,i){"use strict";t.exports=function(t,n,i,e,s){this.message=t,this.transition=n,this.from=i,this.to=e,this.current=s}}])});
\ No newline at end of file
diff --git a/lib/history.js b/lib/history.js
index 19f7c4f..cd50b65 100644
--- a/lib/history.js
+++ b/lib/history.js
@@ -162,6 +162,10 @@ module.exports = function(options) { options = options || {};
       }
     },
 
+    cancel: function(instance, lifecycle) {
+      instance[past].pop()
+    },
+
     methods:    {},
     properties: {}
 
diff --git a/lib/state-machine.js b/lib/state-machine.js
index 4d09915..3177183 100644
--- a/lib/state-machine.js
+++ b/lib/state-machine.js
@@ -465,9 +465,13 @@ mixin(JSM.prototype, {
 
   beginTransit: function()          { this.pending = true;                 },
   endTransit:   function(result)    { this.pending = false; return result; },
-  failTransit:  function(result, from, to) {
+  failTransit:  function(result, args) {
+    var from = args[0].from;
+    var to = args[0].to;
+
     if (this.state === to) {
-       this.state = from;
+      this.state = from;
+      plugin.hook(this, 'cancel', args);
     }
     this.pending = false;
     throw result;
@@ -495,11 +499,11 @@ mixin(JSM.prototype, {
     return [ event, result, true ]
   },
 
-  callObserver: function(event, observer, args, from, to) {
+  callObserver: function(event, observer, args) {
     try {
       return observer[event].apply(observer, args);
     } catch (error) {
-      this.failTransit.call(this, error, from, to);
+      this.failTransit.call(this, error, args);
     }
   },
 
@@ -521,15 +525,13 @@ mixin(JSM.prototype, {
       return this.observeEvents(events, args, event, previousResult);
     }
     else {
-      var from = args[0].from;
-      var to = args[0].to;
       var observer = observers.shift();
-      var result = this.callObserver.call(this, event, observer, args, from, to);
+      var result = this.callObserver.call(this, event, observer, args);
       if (result && typeof result.then === 'function') {
         var jsm = this
         return result.then(this.observeEvents.bind(this, events, args, event))
                      .catch(function (error) {
-                       jsm.failTransit.call(jsm, error, from, to);
+                       jsm.failTransit.call(jsm, error, args);
                      });
       }
       else if (result === false) {