Resource error handling

.github/workflows/ci.yml

@@ -7,6 +7,9 @@ on:
     branches: ["main", "develop"]
   workflow_dispatch:
 
+permissions:
+  contents: write
+
 jobs:
   build:
     runs-on: ubuntu-latest
@@ -20,3 +23,7 @@ jobs:
       - run: npm ci
       - run: npm run build --if-present
       - run: npm test
+      - uses: EndBug/add-and-commit@v7
+        with:
+          commit: "--allow-empty"
+          default_author: github_actions

README.md

@@ -220,11 +220,11 @@ The preferred way of reading a signal is through the `signal.value`.
 
 ## Error Handling
 
-When unhandled errors occur in a `computed` or `effect`, by default, the error will be logged to the console through
-a `console.error` call, and then the error will be rethrown.
+When unhandled errors occur in a `computed`, `effect` or `resource`,
+by default, the error will be logged to the console through a `console.error` call, and then the error will be rethrown.
 
-If you wish to know which `computed` or `effect` caused the error, you can pass a second argument to the `computed` or
-`effect` with a unique identifier.
+If you wish to know where the error is coming from, you can pass a second argument to the `computed`,
+`effect` or `resource` with a unique identifier.
 
 ```javascript
 $computed(
@@ -242,6 +242,14 @@ $effect(
   },
   { identifier: "test-identifier" }
 );
+
+$resource(
+  asyncFunction,
+  {},
+  {
+    identifier: "test-identifier"
+  }
+);
 ```
 
 This value will be used only for debugging purposes, and does not affect the functionality otherwise.
@@ -250,7 +258,7 @@ In this example, the test-identifier string will appear as part of the console.e
 
 ### Custom Error Handlers
 
-Both computed and effect signals can receive a custom `onError` property,
+`computed`, `effect`, and `resource` signals can all receive a custom `onError` property,
 that allows developers to completely override the default functionality that logs and rethrows the error.
 
 #### Effect handlers
@@ -316,6 +324,53 @@ $computed(
 );
 ```
 
+#### Resource handlers
+
+For `resource` handlers, you can pass a function with the following shape:
+
+```typescript
+(error: unknown, previousValue: T | null, options: { initialValue: T | null, identifier: string | symbol }) =>
+        AsyncData<T> | void
+
+// Where AsyncData looks as follows
+// {
+//   data: T | null;
+//   loading: boolean;
+//   error: unknown | null;
+// };
+```
+
+Where you can return nothing, or a value of type `AsyncData<T>`.
+`AsyncData` is the shape that all resources take, and it contains the data, loading state, and error state.
+This allows you to provide a "fallback" value, that the computed value will receive in case of errors.
+
+As a second argument, you will receive the previous value of the resource (or null if there is none), which can be useful to provide a
+fallback value based on the previous value.
+
+The third argument is an object with the received identifier as well as any initial value that was provided to the
+resource when it was created.
+
+Example
+
+```javascript
+function customErrorHandlerFn(error, _previousValue, _options) {
+  // custom logic or logging or rethrowing here
+  return {
+    data: "fallback value",
+    loading: false,
+    error: error
+  };
+}
+
+$resource(
+  asyncFunction,
+  {},
+  {
+    onError: customErrorHandlerFn
+  }
+);
+```
+
 ## Tracking objects and arrays
 
 By default, for a signal to be reactive it needs to be reassigned. This can be cumbersome when dealing with objects
@@ -512,11 +567,11 @@ export default class ContactList extends LightningElement {
 }
 ```
 
-Data from a resource signal comes in the following format:
+Data from a resource signal comes in as a read-only signal in the following format:
 
 ```typescript
 type AsyncData<T> = {
-  data: ReadOnlySignal<T> | null; // The data fetched from the server. It is null until the data is fetched
+  data: T | null; // The data fetched from the server. It is null until the data is fetched
   loading: boolean; // A boolean that indicates if the data is being fetched
   error: unknown | null; // An error object that is populated if the fetch fails
 };

force-app/lwc/signals/core.js

@@ -102,7 +102,7 @@ function $computed(fn, options) {
     () => {
       if (options?.onError) {
         // If this computed has a custom error handler, then the
-        // handling occurs in the computed function itself.
+        // handling occurs here, in the computed function itself.
         try {
           computedSignal.value = fn();
         } catch (error) {
@@ -250,7 +250,22 @@ function $signal(value, options) {
   delete returnValue.unsubscribe;
   return returnValue;
 }
+function defaultResourceErrorHandler(error, _previousValue, options) {
+  const errorTemplate = `
+  LWC Signals: An error occurred in a reactive function \n
+  Type: Resource \n
+  Identifier: ${options.identifier.toString()}
+  `.trim();
+  console.error(errorTemplate, error);
+}
 function $resource(fn, source, options) {
+  const {
+    initialValue = null,
+    optimisticMutate = true,
+    fetchWhen = () => true,
+    identifier = Symbol(),
+    onError = defaultResourceErrorHandler
+  } = options ?? {};
   function loadingState(data) {
     return {
       data: data,
@@ -259,17 +274,14 @@ function $resource(fn, source, options) {
     };
   }
   let _isInitialLoad = true;
-  let _value = options?.initialValue ?? null;
+  let _value = initialValue;
   let _previousParams;
   const _signal = $signal(loadingState(_value));
-  // Optimistic updates are enabled by default
-  const _optimisticMutate = options?.optimisticMutate ?? true;
-  const _fetchWhen = options?.fetchWhen ?? (() => true);
   const execute = async () => {
     const derivedSourceFn = source instanceof Function ? source : () => source;
     try {
       let data = null;
-      if (_fetchWhen()) {
+      if (fetchWhen()) {
         const derivedSource = derivedSourceFn();
         if (!_isInitialLoad && isEqual(derivedSource, _previousParams)) {
           // No need to fetch the data again if the params haven't changed
@@ -289,7 +301,7 @@ function $resource(fn, source, options) {
         error: null
       };
     } catch (error) {
-      _signal.value = {
+      _signal.value = onError(error, _value, { identifier, initialValue }) ?? {
         data: null,
         loading: false,
         error
@@ -298,7 +310,9 @@ function $resource(fn, source, options) {
       _isInitialLoad = false;
     }
   };
-  $effect(execute);
+  $effect(execute, {
+    identifier
+  });
   /**
    * Callback function that updates the value of the resource.
    * @param value The value we want to set the resource to.
@@ -316,7 +330,7 @@ function $resource(fn, source, options) {
     data: _signal.readOnly,
     mutate: (newValue) => {
       const previousValue = _value;
-      if (_optimisticMutate) {
+      if (optimisticMutate) {
         // If optimistic updates are enabled, update the value immediately
         mutatorCallback(newValue);
       }
@@ -327,7 +341,8 @@ function $resource(fn, source, options) {
     refetch: async () => {
       _isInitialLoad = true;
       await execute();
-    }
+    },
+    identifier
   };
 }
 function isSignal(anything) {