Cancel state transition when exception is thrown inside observer

dist/state-machine-history.js

@@ -162,6 +162,10 @@ module.exports = function(options) { options = options || {};
       }
     },
 
+    cancel: function(instance, lifecycle) {
+      instance[past].pop()
+    },
+
     methods:    {},
     properties: {}
 

dist/state-machine.js

@@ -465,7 +465,17 @@ 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, args) {
+    var from = args[0].from;
+    var to = args[0].to;
+
+    if (this.state === to) {
+      this.state = from;
+      plugin.hook(this, 'cancel', args);
+    }
+    this.pending = false;
+    throw result;
+  },
   doTransit:    function(lifecycle) { this.state = lifecycle.to;           },
 
   observe: function(args) {
@@ -489,6 +499,14 @@ mixin(JSM.prototype, {
     return [ event, result, true ]
   },
 
+  callObserver: function(event, observer, args) {
+    try {
+      return observer[event].apply(observer, args);
+    } catch (error) {
+      this.failTransit.call(this, error, args);
+    }
+  },
+
   observeEvents: function(events, args, previousEvent, previousResult) {
     if (events.length === 0) {
       return this.endTransit(previousResult === undefined ? true : previousResult);
@@ -507,11 +525,14 @@ mixin(JSM.prototype, {
       return this.observeEvents(events, args, event, previousResult);
     }
     else {
-      var observer = observers.shift(),
-          result = observer[event].apply(observer, args);
+      var observer = observers.shift();
+      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(this.failTransit.bind(this))
+                     .catch(function (error) {
+                       jsm.failTransit.call(jsm, error, args);
+                     });
       }
       else if (result === false) {
         return this.endTransit(false);

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
+

lib/history.js

@@ -162,6 +162,10 @@ module.exports = function(options) { options = options || {};
       }
     },
 
+    cancel: function(instance, lifecycle) {
+      instance[past].pop()
+    },
+
     methods:    {},
     properties: {}
 

lib/state-machine.js

@@ -465,7 +465,17 @@ 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, args) {
+    var from = args[0].from;
+    var to = args[0].to;
+
+    if (this.state === to) {
+      this.state = from;
+      plugin.hook(this, 'cancel', args);
+    }
+    this.pending = false;
+    throw result;
+  },
   doTransit:    function(lifecycle) { this.state = lifecycle.to;           },
 
   observe: function(args) {
@@ -489,6 +499,14 @@ mixin(JSM.prototype, {
     return [ event, result, true ]
   },
 
+  callObserver: function(event, observer, args) {
+    try {
+      return observer[event].apply(observer, args);
+    } catch (error) {
+      this.failTransit.call(this, error, args);
+    }
+  },
+
   observeEvents: function(events, args, previousEvent, previousResult) {
     if (events.length === 0) {
       return this.endTransit(previousResult === undefined ? true : previousResult);
@@ -507,11 +525,14 @@ mixin(JSM.prototype, {
       return this.observeEvents(events, args, event, previousResult);
     }
     else {
-      var observer = observers.shift(),
-          result = observer[event].apply(observer, args);
+      var observer = observers.shift();
+      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(this.failTransit.bind(this))
+                     .catch(function (error) {
+                       jsm.failTransit.call(jsm, error, args);
+                     });
       }
       else if (result === false) {
         return this.endTransit(false);

src/jsm.js

@@ -108,7 +108,17 @@ 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, args) {
+    var from = args[0].from;
+    var to = args[0].to;
+
+    if (this.state === to) {
+      this.state = from;
+      plugin.hook(this, 'cancel', args);
+    }
+    this.pending = false;
+    throw result;
+  },
   doTransit:    function(lifecycle) { this.state = lifecycle.to;           },
 
   observe: function(args) {
@@ -132,6 +142,14 @@ mixin(JSM.prototype, {
     return [ event, result, true ]
   },
 
+  callObserver: function(event, observer, args) {
+    try {
+      return observer[event].apply(observer, args);
+    } catch (error) {
+      this.failTransit.call(this, error, args);
+    }
+  },
+
   observeEvents: function(events, args, previousEvent, previousResult) {
     if (events.length === 0) {
       return this.endTransit(previousResult === undefined ? true : previousResult);
@@ -150,11 +168,14 @@ mixin(JSM.prototype, {
       return this.observeEvents(events, args, event, previousResult);
     }
     else {
-      var observer = observers.shift(),
-          result = observer[event].apply(observer, args);
+      var observer = observers.shift();
+      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(this.failTransit.bind(this))
+                     .catch(function (error) {
+                       jsm.failTransit.call(jsm, error, args);
+                     });
       }
       else if (result === false) {
         return this.endTransit(false);

src/plugin/history.js

@@ -39,6 +39,10 @@ module.exports = function(options) { options = options || {};
       }
     },
 
+    cancel: function(instance, lifecycle) {
+      instance[past].pop()
+    },
+
     methods:    {},
     properties: {}
 

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')
+})

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')
+})