Add 'watchFn' for more flexibility in reloading based on prop changes.

README.md

@@ -40,7 +40,7 @@ without assumptions about the shape of your data or the type of request.
 - Choose between Render Props, Context-based helper components or the `useAsync` hook
 - Provides convenient `isLoading`, `startedAt` and `finishedAt` metadata
 - Provides `cancel` and `reload` actions
-- Automatic re-run using `watch` prop
+- Automatic re-run using `watch` or `watchFn` prop
 - Accepts `onResolve` and `onReject` callbacks
 - Supports [abortable fetch] by providing an AbortController
 - Supports optimistic updates using `setData`
@@ -205,6 +205,7 @@ The shorthand version currently does not support passing additional props.
 - `promiseFn` {(props, controller) => Promise} A function that returns a promise; invoked in `componentDidMount` and `componentDidUpdate`; receives component props (object) and AbortController instance as arguments
 - `deferFn` {(...args, props, controller) => Promise} A function that returns a promise; invoked only by calling `run(...args)`, with arguments being passed through, as well as component props (object) and AbortController as final arguments
 - `watch` {any} Watches this property through `componentDidUpdate` and re-runs the `promiseFn` when the value changes (`oldValue !== newValue`)
+- `watchFn` {(props, prevProps) => any} Re-runs the `promiseFn` when this callback returns truthy (called on every update).
 - `initialValue` {any} initial state for `data` or `error` (if instance of Error); useful for server-side rendering
 - `onResolve` {Function} Callback function invoked when a promise resolves, receives data as argument
 - `onReject` {Function} Callback function invoked when a promise rejects, receives error as argument

src/index.js

@@ -56,9 +56,11 @@ export const createInstance = (defaultProps = {}, displayName = "Async") => {
     }
 
     componentDidUpdate(prevProps) {
-      if (prevProps.watch !== this.props.watch) this.load()
-      if (prevProps.promiseFn !== this.props.promiseFn) {
-        if (this.props.promiseFn) this.load()
+      const { watch, watchFn, promiseFn } = this.props
+      if (watch !== prevProps.watch) this.load()
+      if (watchFn && watchFn(this.props, prevProps)) this.load()
+      if (promiseFn !== prevProps.promiseFn) {
+        if (promiseFn) this.load()
         else this.cancel()
       }
     }

src/spec.js

@@ -129,6 +129,33 @@ describe("Async", () => {
     expect(abortCtrl.abort).toHaveBeenCalledTimes(2)
   })
 
+  test("re-runs the promise when 'watchFn' returns truthy", () => {
+    class Counter extends React.Component {
+      state = { count: 0 }
+      inc = () => this.setState(state => ({ count: state.count + 1 }))
+      render() {
+        return (
+          <div>
+            <button onClick={this.inc}>increment</button>
+            {this.props.children(this.state.count)}
+          </div>
+        )
+      }
+    }
+    const promiseFn = jest.fn().mockReturnValue(resolveTo())
+    const watchFn = ({ count }, prevProps) => count !== prevProps.count && count === 2
+    const { getByText } = render(
+      <Counter>{count => <Async promiseFn={promiseFn} watchFn={watchFn} count={count} />}</Counter>
+    )
+    expect(promiseFn).toHaveBeenCalledTimes(1)
+    fireEvent.click(getByText("increment"))
+    expect(promiseFn).toHaveBeenCalledTimes(1)
+    expect(abortCtrl.abort).toHaveBeenCalledTimes(0)
+    fireEvent.click(getByText("increment"))
+    expect(promiseFn).toHaveBeenCalledTimes(2)
+    expect(abortCtrl.abort).toHaveBeenCalledTimes(1)
+  })
+
   test("runs deferFn only when explicitly invoked, passing arguments, props and AbortController", () => {
     let counter = 1
     const deferFn = jest.fn().mockReturnValue(resolveTo())

src/useAsync.js

@@ -4,10 +4,11 @@ const useAsync = (opts, init) => {
   const counter = useRef(0)
   const isMounted = useRef(true)
   const lastArgs = useRef(undefined)
+  const prevOptions = useRef(undefined)
   const abortController = useRef({ abort: () => {} })
 
   const options = typeof opts === "function" ? { promiseFn: opts, initialValue: init } : opts
-  const { promiseFn, deferFn, initialValue, onResolve, onReject, watch } = options
+  const { promiseFn, deferFn, initialValue, onResolve, onReject, watch, watchFn } = options
 
   const [state, setState] = useState({
     data: initialValue instanceof Error ? undefined : initialValue,
@@ -76,9 +77,13 @@ const useAsync = (opts, init) => {
     setState(state => ({ ...state, startedAt: undefined }))
   }
 
+  useEffect(() => {
+    if (watchFn && prevOptions.current && watchFn(options, prevOptions.current)) load()
+  })
   useEffect(() => (promiseFn ? load() && undefined : cancel()), [promiseFn, watch])
   useEffect(() => () => (isMounted.current = false), [])
   useEffect(() => abortController.current.abort, [])
+  useEffect(() => (prevOptions.current = options) && undefined)
 
   return useMemo(
     () => ({

src/useAsync.spec.js

@@ -127,6 +127,37 @@ describe("useAsync", () => {
     expect(abortCtrl.abort).toHaveBeenCalledTimes(2)
   })
 
+  test("re-runs the promise when 'watchFn' returns truthy", () => {
+    class Counter extends React.Component {
+      state = { count: 0 }
+      inc = () => this.setState(state => ({ count: state.count + 1 }))
+      render() {
+        return (
+          <div>
+            <button onClick={this.inc}>increment</button>
+            {this.props.children(this.state.count)}
+          </div>
+        )
+      }
+    }
+    const promiseFn = jest.fn().mockReturnValue(resolveTo())
+    const watchFn = ({ count }, prevProps) => count !== prevProps.count && count === 2
+    const component = (
+      <Counter>{count => <Async promiseFn={promiseFn} watchFn={watchFn} count={count} />}</Counter>
+    )
+    const { getByText } = render(component)
+    flushEffects()
+    expect(promiseFn).toHaveBeenCalledTimes(1)
+    fireEvent.click(getByText("increment"))
+    flushEffects()
+    expect(promiseFn).toHaveBeenCalledTimes(1)
+    expect(abortCtrl.abort).toHaveBeenCalledTimes(0)
+    fireEvent.click(getByText("increment"))
+    flushEffects()
+    expect(promiseFn).toHaveBeenCalledTimes(2)
+    expect(abortCtrl.abort).toHaveBeenCalledTimes(1)
+  })
+
   test("runs deferFn only when explicitly invoked, passing arguments and props", () => {
     let counter = 1
     const deferFn = jest.fn().mockReturnValue(resolveTo())