feat: Support populateCache as a function

examples/optimistic-ui/libs/fetch.js

@@ -1,4 +1,5 @@
 export default async function fetcher(...args) {
   const res = await fetch(...args)
+  if (!res.ok) throw new Error('Failed to fetch')
   return res.json()
 }

examples/optimistic-ui/pages/_app.js

@@ -0,0 +1,5 @@
+import '../styles.css'
+
+export default function App({ Component, pageProps }) {
+  return <Component {...pageProps} />
+}

examples/optimistic-ui/pages/api/todos.js

@@ -0,0 +1,30 @@
+let todos = []
+const delay = () => new Promise(res => setTimeout(() => res(), 1000))
+
+async function getTodos() {
+  await delay()
+  return todos.sort((a, b) => (a.text < b.text ? -1 : 1))
+}
+
+async function addTodo(todo) {
+  await delay()
+  // Sometimes it will fail, this will cause a regression on the UI
+  if (Math.random() < 0.2 || !todo.text)
+    throw new Error('Failed to add new item!')
+  todo.text = todo.text.charAt(0).toUpperCase() + todo.text.slice(1)
+  todos = [...todos, todo]
+  return todo
+}
+
+export default async function api(req, res) {
+  try {
+    if (req.method === 'POST') {
+      const body = JSON.parse(req.body)
+      return res.json(await addTodo(body))
+    }
+
+    return res.json(await getTodos())
+  } catch (err) {
+    return res.status(500).json({ error: err.message })
+  }
+}

examples/optimistic-ui/pages/index.js

@@ -1,41 +1,110 @@
-import React from 'react'
+import useSWR from 'swr'
+import React, { useState } from 'react'
+
 import fetch from '../libs/fetch'
 
-import useSWR, { mutate } from 'swr'
-
-export default function Index() {
-  const [text, setText] = React.useState('');
-  const { data } = useSWR('/api/data', fetch)
-
-  async function handleSubmit(event) {
-    event.preventDefault()
-    // Call mutate to optimistically update the UI.
-    mutate('/api/data', [...data, text], false)
-    // Then we send the request to the API and let mutate
-    // update the data with the API response.
-    // Our action may fail in the API function, and the response differ
-    // from what was optimistically updated, in that case the UI will be
-    // changed to match the API response.
-    // The fetch could also fail, in that case the UI will
-    // be in an incorrect state until the next successful fetch.
-    mutate('/api/data', await fetch('/api/data', {
-      method: 'POST',
-      body: JSON.stringify({ text })
-    }))
-    setText('')
-  }
-
-  return <div>
-    <form onSubmit={handleSubmit}>
-      <input
-        type="text"
-        onChange={event => setText(event.target.value)}
-        value={text}
-      />
-      <button>Create</button>
-    </form>
-    <ul>
-      {data ? data.map(datum => <li key={datum}>{datum}</li>) : 'loading...'}
-    </ul>
-  </div>
+export default function App() {
+  const [text, setText] = useState('')
+  const { data, mutate } = useSWR('/api/todos', fetch)
+
+  const [state, setState] = useState(<span className="info">&nbsp;</span>)
+
+  return (
+    <div>
+      {/* <Toaster toastOptions={{ position: 'bottom-center' }} /> */}
+      <h1>Optimistic UI with SWR</h1>
+
+      <p className="note">
+        <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24">
+          <path d="M12 2c5.514 0 10 4.486 10 10s-4.486 10-10 10-10-4.486-10-10 4.486-10 10-10zm0-2c-6.627 0-12 5.373-12 12s5.373 12 12 12 12-5.373 12-12-5.373-12-12-12zm1 18h-2v-8h2v8zm-1-12.25c.69 0 1.25.56 1.25 1.25s-.56 1.25-1.25 1.25-1.25-.56-1.25-1.25.56-1.25 1.25-1.25z" />
+        </svg>
+        This application optimistically updates the data, while revalidating in
+        the background. The <code>POST</code> API auto capitializes the data,
+        and only returns the new added one instead of the full list. And the{' '}
+        <code>GET</code> API returns the full list in order.
+      </p>
+
+      <form onSubmit={ev => ev.preventDefault()}>
+        <input
+          value={text}
+          onChange={e => setText(e.target.value)}
+          placeholder="Add your to-do here..."
+          autoFocus
+        />
+        <button
+          type="submit"
+          onClick={async () => {
+            setText('')
+            setState(
+              <span className="info">Showing optimistic data, mutating...</span>
+            )
+
+            const newTodo = {
+              id: Date.now(),
+              text
+            }
+
+            try {
+              // Update the local state immediately and fire the
+              // request. Since the API will return the updated
+              // data, there is no need to start a new revalidation
+              // and we can directly populate the cache.
+              await mutate(
+                fetch('/api/todos', {
+                  method: 'POST',
+                  body: JSON.stringify(newTodo)
+                }),
+                {
+                  optimisticData: [...data, newTodo],
+                  rollbackOnError: true,
+                  populateCache: newItem => {
+                    setState(
+                      <span className="success">
+                        Succesfully mutated the resource and populated cache.
+                        Revalidating...
+                      </span>
+                    )
+
+                    return [...data, newItem]
+                  },
+                  revalidate: true
+                }
+              )
+              setState(<span className="info">Revalidated the resource.</span>)
+            } catch (e) {
+              // If the API errors, the original data will be
+              // rolled back by SWR automatically.
+              setState(
+                <span className="error">
+                  Failed to mutate. Rolled back to previous state and
+                  revalidated the resource.
+                </span>
+              )
+            }
+          }}
+        >
+          Add
+        </button>
+      </form>
+
+      {state}
+
+      <ul>
+        {data ? (
+          data.length ? (
+            data.map(todo => {
+              return <li key={todo.id}>{todo.text}</li>
+            })
+          ) : (
+            <i>
+              No todos yet. Try adding lowercased "banana" and "apple" to the
+              list.
+            </i>
+          )
+        ) : (
+          <i>Loading...</i>
+        )}
+      </ul>
+    </div>
+  )
 }

examples/optimistic-ui/styles.css

@@ -0,0 +1,91 @@
+html {
+  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen,
+    Ubuntu, Cantarell, 'Open Sans', 'Helvetica Neue', sans-serif;
+  text-align: center;
+}
+
+body {
+  max-width: 600px;
+  margin: auto;
+}
+
+h1 {
+  margin-top: 1em;
+}
+
+.note {
+  text-align: left;
+  font-size: 0.9em;
+  line-height: 1.5;
+  color: #666;
+}
+
+.note svg {
+  margin-right: 0.5em;
+  vertical-align: -2px;
+  width: 14px;
+  height: 14px;
+  margin-right: 5px;
+}
+
+form {
+  display: flex;
+  margin: 8px 0;
+  gap: 8px;
+}
+
+input {
+  flex: 1;
+}
+
+input,
+button {
+  font-size: 16px;
+  padding: 6px 5px;
+}
+
+code {
+  font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas,
+    Liberation Mono, Courier New, monospace;
+  font-feature-settings: 'rlig' 1, 'calt' 1, 'ss01' 1;
+  background-color: #eee;
+  padding: 1px 3px;
+  border-radius: 2px;
+}
+
+ul {
+  text-align: left;
+  list-style: none;
+  padding: 0;
+}
+
+li {
+  margin: 8px 0;
+  padding: 10px;
+  border-radius: 4px;
+  box-shadow: 0 2px 6px rgba(0, 0, 0, 0.12), 0 0 0 1px #ededed;
+}
+
+i {
+  color: #999;
+}
+
+.info,
+.success,
+.error {
+  display: block;
+  text-align: left;
+  padding: 6px 0;
+  font-size: 0.9em;
+  opacity: 0.9;
+}
+
+.info {
+  color: #666;
+}
+.success {
+  color: #4caf50;
+}
+.error {
+  color: #f44336;
+}

package.json

@@ -97,7 +97,7 @@
     "husky": "2.4.1",
     "jest": "27.0.6",
     "lint-staged": "8.2.1",
-    "next": "12.0.9",
+    "next": "^12.1.0",
     "npm-run-all": "4.1.5",
     "prettier": "2.5.0",
     "react": "17.0.1",
@@ -112,11 +112,11 @@
     "react": "^16.11.0 || ^17.0.0 || ^18.0.0"
   },
   "prettier": {
+    "tabWidth": 2,
     "semi": false,
-    "singleQuote": true,
     "useTabs": false,
-    "trailingComma": "none",
-    "tabWidth": 2,
-    "arrowParens": "avoid"
+    "singleQuote": true,
+    "arrowParens": "avoid",
+    "trailingComma": "none"
   }
 }

src/types.ts

@@ -139,12 +139,12 @@ export type Arguments =
 export type Key = Arguments | (() => Arguments)
 
 export type MutatorCallback<Data = any> = (
-  currentValue?: Data
+  currentData?: Data
 ) => Promise<undefined | Data> | undefined | Data
 
 export type MutatorOptions<Data = any> = {
   revalidate?: boolean
-  populateCache?: boolean
+  populateCache?: boolean | ((result: any, currentData: Data) => Data)
   optimisticData?: Data
   rollbackOnError?: boolean
 }

src/use-swr.ts

@@ -360,7 +360,9 @@ export const useSWRHandler = <Data = any, Error = any>(
   // eslint-disable-next-line react-hooks/exhaustive-deps
   const boundMutate: SWRResponse<Data, Error>['mutate'] = useCallback(
     // By using `bind` we don't need to modify the size of the rest arguments.
-    internalMutate.bind(UNDEFINED, cache, () => keyRef.current),
+    // Due to https://github.com/microsoft/TypeScript/issues/37181, we have to
+    // cast it to any for now.
+    internalMutate.bind(UNDEFINED, cache, () => keyRef.current) as any,
     // eslint-disable-next-line react-hooks/exhaustive-deps
     []
   )

src/utils/helper.ts

@@ -4,7 +4,7 @@ export const noop = () => {}
 // by something else.  Prettier ignore and extra parentheses are necessary here
 // to ensure that tsc doesn't remove the __NOINLINE__ comment.
 // prettier-ignore
-export const UNDEFINED: undefined = (/*#__NOINLINE__*/ noop()) as undefined
+export const UNDEFINED = (/*#__NOINLINE__*/ noop()) as undefined
 
 export const OBJECT = Object