Add useAsync hook to leverage new Hooks proposal

.travis.yml

@@ -4,6 +4,6 @@ node_js:
 cache:
   directories:
     - node_modules
-script: npm run test:compat
+script: npm run test:compat && npm run test:hook
 after_success:
   - bash <(curl -s https://codecov.io/bash) -e TRAVIS_NODE_VERSION

README.md

@@ -31,13 +31,13 @@
   </a>
 </p>
 
-React component for declarative promise resolution and data fetching. Leverages the Render Props pattern for ultimate
-flexibility as well as the new Context API for ease of use. Makes it easy to handle loading and error states, without
-assumptions about the shape of your data or the type of request.
+React component for declarative promise resolution and data fetching. Leverages the Render Props pattern and Hooks for
+ultimate flexibility as well as the new Context API for ease of use. Makes it easy to handle loading and error states,
+without assumptions about the shape of your data or the type of request.
 
 - Zero dependencies
 - Works with any (native) promise
-- Choose between Render Props and Context-based helper components
+- 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
@@ -84,6 +84,37 @@ npm install --save react-async
 
 ## Usage
 
+As a hook with `useAsync`:
+
+```js
+import { useAsync } from "react-async"
+
+const loadJson = () => fetch("/some/url").then(res => res.json())
+
+const MyComponent = () => {
+  const { data, error, isLoading } = useAsync({ promiseFn: loadJson })
+  if (isLoading) return "Loading..."
+  if (error) return `Something went wrong: ${error.message}`
+  if (data)
+    return (
+      <div>
+        <strong>Loaded some data:</strong>
+        <pre>{JSON.stringify(data, null, 2)}</pre>
+      </div>
+    )
+  return null
+}
+```
+
+Or using the shorthand version:
+
+```js
+const MyComponent = () => {
+  const { data, error, isLoading } = useAsync(loadJson)
+  // ...
+}
+```
+
 Using render props for ultimate flexibility:
 
 ```js
@@ -186,6 +217,14 @@ Similarly, this allows you to set default `onResolve` and `onReject` callbacks.
 - `setData` {Function} sets `data` to the passed value, unsets `error` and cancels any pending promise
 - `setError` {Function} sets `error` to the passed value and cancels any pending promise
 
+### `useState`
+
+The `useState` hook accepts an object with the same props as `<Async>`. Alternatively you can use the shorthand syntax:
+
+```js
+useState(promiseFn, initialValue)
+```
+
 ## Examples
 
 ### Basic data fetching with loading indicator, error state and retry

package.json

@@ -26,15 +26,16 @@
     "typings"
   ],
   "scripts": {
-    "build": "babel src -d lib",
+    "build": "rimraf lib && babel src -d lib --ignore '**/*spec.js'",
     "lint": "eslint src",
-    "test": "jest src",
+    "test": "jest src/spec.js  --collectCoverageFrom=src/index.js",
     "test:watch": "npm run test -- --watch",
     "test:compat": "npm run test:backwards && npm run test:forwards && npm run test:latest",
     "test:backwards": "npm i [email protected] [email protected] && npm test",
     "test:forwards": "npm i react@next react-dom@next && npm test",
     "test:latest": "npm i react@latest react-dom@latest && npm test",
-    "prepublishOnly": "npm run lint && npm run test:compat && npm run build"
+    "test:hook": "npm i [email protected] [email protected] && jest src/useAsync.spec.js --collectCoverageFrom=src/useAsync.js",
+    "prepublishOnly": "npm run lint && npm run test:compat && npm run test:hook && npm run build"
   },
   "dependencies": {},
   "peerDependencies": {
@@ -58,7 +59,8 @@
     "prettier": "1.15.3",
     "react": "16.6.3",
     "react-dom": "16.6.3",
-    "react-testing-library": "5.2.3"
+    "react-testing-library": "5.4.2",
+    "rimraf": "2.6.2"
   },
   "jest": {
     "coverageDirectory": "./coverage/",

src/index.js

@@ -1,4 +1,5 @@
 import React from "react"
+export { default as useAsync } from "./useAsync"
 
 const isFunction = arg => typeof arg === "function"
 

src/useAsync.js

@@ -0,0 +1,89 @@
+import { useState, useEffect, useMemo, useRef } from "react"
+
+const useAsync = (opts, init) => {
+  const counter = useRef(0)
+  const isMounted = useRef(true)
+  const lastArgs = useRef(undefined)
+
+  const options = typeof opts === "function" ? { promiseFn: opts, initialValue: init } : opts
+  const { promiseFn, deferFn, initialValue, onResolve, onReject, watch } = options
+
+  const [state, setState] = useState({
+    data: initialValue instanceof Error ? undefined : initialValue,
+    error: initialValue instanceof Error ? initialValue : undefined,
+    startedAt: promiseFn ? new Date() : undefined,
+    finishedAt: initialValue ? new Date() : undefined,
+  })
+
+  const handleData = (data, callback = () => {}) => {
+    if (isMounted.current) {
+      setState(state => ({ ...state, data, error: undefined, finishedAt: new Date() }))
+      callback(data)
+    }
+    return data
+  }
+
+  const handleError = (error, callback = () => {}) => {
+    if (isMounted.current) {
+      setState(state => ({ ...state, error, finishedAt: new Date() }))
+      callback(error)
+    }
+    return error
+  }
+
+  const handleResolve = count => data => count === counter.current && handleData(data, onResolve)
+  const handleReject = count => error => count === counter.current && handleError(error, onReject)
+
+  const start = () => {
+    counter.current++
+    setState(state => ({
+      ...state,
+      startedAt: new Date(),
+      finishedAt: undefined,
+    }))
+  }
+
+  const load = () => {
+    const isPreInitialized = initialValue && counter.current === 0
+    if (promiseFn && !isPreInitialized) {
+      start()
+      promiseFn(options).then(handleResolve(counter.current), handleReject(counter.current))
+    }
+  }
+
+  const run = (...args) => {
+    if (deferFn) {
+      start()
+      lastArgs.current = args
+      return deferFn(...args, options).then(handleResolve(counter.current), handleReject(counter.current))
+    }
+  }
+
+  useEffect(load, [promiseFn, watch])
+  useEffect(() => () => (isMounted.current = false), [])
+
+  return useMemo(
+    () => ({
+      ...state,
+      isLoading: state.startedAt && (!state.finishedAt || state.finishedAt < state.startedAt),
+      initialValue,
+      run,
+      reload: () => (lastArgs.current ? run(...lastArgs.current) : load()),
+      cancel: () => {
+        counter.current++
+        setState(state => ({ ...state, startedAt: undefined }))
+      },
+      setData: handleData,
+      setError: handleError,
+    }),
+    [state]
+  )
+}
+
+const unsupported = () => {
+  throw new Error(
+    "useAsync requires [email protected]. Upgrade your React version or use the <Async> component instead."
+  )
+}
+
+export default (useState ? useAsync : unsupported)