add `(un)subscribe` function

build.mjs

@@ -0,0 +1,10 @@
+import * as esbuild from 'esbuild'
+
+await esbuild.build({
+  entryPoints: ['src/index.ts'],
+  bundle: true,
+  sourcemap: true,
+  minify: true,
+  format: 'esm',
+  outdir: 'dist',
+})

dist/index.js

@@ -1,2 +1,2 @@
-var d=function(...t){return{states:t}},y=function(t,...e){return{name:t,ons:e}},v=function(t,...e){return{eventName:t,reactions:e}},D=function(t){return{type:"Do",fn:t}},k=function(t){return{type:"Goto",targetStateName:t}},c=function(t){return{doFunctions:t}};function l(t,e){let{state:o,context:s}=e;return typeof o>"u"&&(o=t.states[0].name),{machine:t,state:o,context:s,tickQueues:[]}}function i(t){return t.machine.states.find(e=>e.name===t.state)}function _(t,e){return t.ons.filter(o=>o.eventName===e[0])}function C(){}function G(t,e){let o=i(t),r=_(o,e).map(n=>n.reactions).flat(),a=r.findIndex(n=>n.type==="Goto"),E=a===-1?r.length-1:a,S=r.slice(0,E+1).map(n=>n.type==="Do"?n.fn:n.type==="Goto"?(p,f,T)=>{T.state=n.targetStateName}:C);c(S).doFunctions.forEach(n=>{n(t.context,e,t)})}var m=function(){},A=function(){};export{D as Do,k as Goto,d as Machine,v as On,m as Spawn,y as State,A as Unspawn,l as interpret,G as send};
+var l=function(...t){return{states:t}},g=function(t,...n){return{name:t,eventReactionCouplings:n}},y=function(t,...n){return{eventName:t,reactions:n}},E=function(t){return{type:"SideEffect",fn:t}},S=function(t){return{type:"Goto",targetStateName:t}},v=function(t){return{type:"ContextMutation",fn:t}};function d(t,n){let{state:e,context:i}=n;typeof e>"u"&&(e=t.states[0].name);let o={machine:t,state:e,context:i,eventQueue:[],isTransitioning:!1,subscriptions:{}};return c(o,["entry",null]),o}function T(t){return t.machine.states.find(n=>n.name===t.state)}function p(t,n){return t.eventReactionCouplings.filter(e=>e.eventName===n[0])}function c(t,n){if(t.eventQueue.push(n),t.isTransitioning===!1){for(t.isTransitioning=!0;t.eventQueue.length>0;)_(t);t.isTransitioning=!1,Object.values(t.subscriptions).forEach(e=>{e(t)})}}var C=c;function _(t){let n=t.eventQueue.shift();if(typeof n<"u"){let e=T(t),o=p(e,n).map(a=>a.reactions).flat(),{sideEffects:u,contextMutations:f,goto_:r}=x(o);u.forEach(a=>{a.fn(t.context,n,t)}),f.forEach(a=>{t.context=a.fn(t.context,n,t)}),r!==null&&(c(t,["exit",null]),t.state=r.targetStateName,c(t,["entry",null]))}}function x(t){let n=[],e=[],i=null;return t.forEach(o=>{o.type==="SideEffect"?n.push(o):o.type==="ContextMutation"?e.push(o):o.type==="Goto"&&(i=o)}),{sideEffects:n,contextMutations:e,goto_:i}}var s=0;function M(t,n){return s++,t.subscriptions[s.toString()]=n,s}function b(t,n){delete t.subscriptions[n.toString()]}var h=function(){},R=function(){};export{v as Context,S as Goto,l as Machine,y as On,E as SideEffect,h as Spawn,g as State,R as Unspawn,C as enqueue,d as interpret,c as send,M as subscribe,b as unsubscribe};
 //# sourceMappingURL=index.js.map

src/index.ts

@@ -43,11 +43,12 @@ export interface Interpreter_T {
   context: any;
   eventQueue:Array<Event_T>;
   isTransitioning: boolean;
+  subscriptions: Record<string, SubscriptionCallbackFunction_T>
 }
 export function interpret(machine:Machine_T, options:{state?:string, context:any}) : Interpreter_T{
   let {state, context} = options;
   if(typeof state === 'undefined'){ state = machine.states[0].name; }
-  const interpreter = {machine, state, context, eventQueue:[], isTransitioning:false}
+  const interpreter = {machine, state, context, eventQueue:[], isTransitioning:false, subscriptions: {}}
   send(interpreter, ['entry', null] );
   return interpreter;
 }
@@ -80,6 +81,8 @@ export function send(interpreter : Interpreter_T, event:Event_T){
       processNextEvent(interpreter);
     }
     interpreter.isTransitioning = false;
+    // only run subscriptions here, once the machine's state has settled:
+    Object.values(interpreter.subscriptions).forEach((subscriptionCallbackFunction)=>{ subscriptionCallbackFunction(interpreter); });
   }
 }
 export const enqueue = send;
@@ -102,6 +105,7 @@ function processNextEvent(interpreter:Interpreter_T){
     });
     // processing of `goto` must be last:
     if(goto_ !== null){
+      send(interpreter, ['exit', null]);
       interpreter.state = goto_.targetStateName;
       send(interpreter, ['entry', null]);
     }
@@ -126,5 +130,22 @@ function categorizeReactions(reactions:Array<Reaction_T>) : {sideEffects:Array<S
   return {sideEffects, contextMutations, goto_};
 }
 
+export type SubscriptionCallbackFunction_T = (self:Interpreter_T)=>void;
+let subscriptionId : number = 0;
+export function subscribe(interpreter:Interpreter_T, callback:SubscriptionCallbackFunction_T){
+  subscriptionId++;
+  interpreter.subscriptions[subscriptionId.toString()] = callback;
+  return subscriptionId;
+}
+export function unsubscribe(interpreter:Interpreter_T, subscriptionId:string){
+  delete interpreter.subscriptions[subscriptionId.toString()];
+}
+
 export const Spawn = function(){};
-export const Unspawn = function(){};
+export const Unspawn = function(){};
+
+/*
+export function useMachine(machine, options){
+  return useMemo(()=>interpret(AppMachine, {context:{}}),[]);
+}
+*/

tsconfig.json

@@ -0,0 +1,7 @@
+{
+  "compilerOptions": {
+    "emitDeclarationOnly": true,
+    "declaration": true,
+    "lib": ["ES2020"]
+  }
+}