update @types/node, docs on allowStaleOnFetchAbort

README.md

@@ -264,8 +264,32 @@ Set to true to return a stale value from the cache when the
 event, whether user-triggered, or due to internal cache behavior.
 
 Unless `ignoreFetchAbort` is also set, the underlying
-`fetchMethod` will still be considered canceled, and its return
-value will be ignored and not cached.
+`fetchMethod` will still be considered canceled, and any value
+it returns will be ignored and not cached.
+
+Caveat: since fetches are aborted when a new value is explicitly
+set in the cache, this can lead to fetch returning a stale value,
+since that was the fallback value _at the moment the `fetch()` was
+initiated_, even though the new updated value is now present in
+the cache.
+
+For example:
+
+```ts
+const cache = new LRUCache<string, any>({
+  ttl: 100,
+  fetchMethod: async (url, oldValue, { signal }) =>  {
+    const res = await fetch(url, { signal })
+    return await res.json()
+  }
+})
+cache.set('https://example.com/', { some: 'data' })
+// 100ms go by...
+const result = cache.fetch('https://example.com/')
+cache.set('https://example.com/', { other: 'thing' })
+console.log(await result) // { some: 'data' }
+console.log(cache.get('https://example.com/')) // { other: 'thing' }
+```
 
 ### `ignoreFetchAbort`
 
@@ -569,7 +593,7 @@ For the usage of the `status` option, see **Status Tracking**
 below.
 
 If the value is `undefined`, then this is an alias for
-`cache.delete(key)`.  `undefined` is never stored in the cache.
+`cache.delete(key)`. `undefined` is never stored in the cache.
 See **Storing Undefined Values** below.
 
 ### `get(key, { updateAgeOnGet, allowStale, status } = {}) => value`
@@ -1028,7 +1052,7 @@ internally in a few places to indicate that a key is not in the
 cache.
 
 You may call `cache.set(key, undefined)`, but this is just an
-an alias for `cache.delete(key)`.  Note that this has the effect
+an alias for `cache.delete(key)`. Note that this has the effect
 that `cache.has(key)` will return _false_ after setting it to
 undefined.
 

package.json

@@ -56,7 +56,7 @@
   "repository": "git://github.com/isaacs/node-lru-cache.git",
   "devDependencies": {
     "@size-limit/preset-small-lib": "^7.0.8",
-    "@types/node": "^17.0.31",
+    "@types/node": "^20.2.5",
     "@types/tap": "^15.0.6",
     "benchmark": "^2.1.4",
     "c8": "^7.11.2",

src/index.ts

@@ -712,8 +712,32 @@ export namespace LRUCache {
      * event, whether user-triggered, or due to internal cache behavior.
      *
      * Unless {@link OptionsBase.ignoreFetchAbort} is also set, the underlying
-     * {@link OptionsBase.fetchMethod} will still be considered canceled, and its return
-     * value will be ignored and not cached.
+     * {@link OptionsBase.fetchMethod} will still be considered canceled, and
+     * any value it returns will be ignored and not cached.
+     *
+     * Caveat: since fetches are aborted when a new value is explicitly
+     * set in the cache, this can lead to fetch returning a stale value,
+     * since that was the fallback value _at the moment the `fetch()` was
+     * initiated_, even though the new updated value is now present in
+     * the cache.
+     *
+     * For example:
+     *
+     * ```ts
+     * const cache = new LRUCache<string, any>({
+     *   ttl: 100,
+     *   fetchMethod: async (url, oldValue, { signal }) =>  {
+     *     const res = await fetch(url, { signal })
+     *     return await res.json()
+     *   }
+     * })
+     * cache.set('https://example.com/', { some: 'data' })
+     * // 100ms go by...
+     * const result = cache.fetch('https://example.com/')
+     * cache.set('https://example.com/', { other: 'thing' })
+     * console.log(await result) // { some: 'data' }
+     * console.log(cache.get('https://example.com/')) // { other: 'thing' }
+     * ```
      */
     allowStaleOnFetchAbort?: boolean
 

test/fetch.ts

@@ -647,7 +647,8 @@ t.test('abort, but then keep on fetching anyway', async t => {
       return new Promise(res =>
         setTimeout(() => {
           resolved = true
-          res(returnUndefined ? undefined : k)
+          if (returnUndefined) res()
+          else res(k)
         }, 100)
       )
     },
@@ -706,7 +707,10 @@ t.test('allowStaleOnFetchAbort', async t => {
     fetchMethod: async (k, _, { signal }) => {
       return new Promise(res => {
         const t = setTimeout(() => res(k), 100)
-        signal.addEventListener('abort', () => clearTimeout(t))
+        signal.addEventListener('abort', () => {
+          clearTimeout(t)
+          res()
+        })
       })
     },
   })
@@ -716,7 +720,11 @@ t.test('allowStaleOnFetchAbort', async t => {
   const p = c.fetch(1, { signal: ac.signal })
   ac.abort(new Error('gimme the stale value'))
   t.equal(await p, 10)
-  t.equal(c.get(1, { allowStale: true }), 10)
+  t.equal(c.get(1, { allowStale: true, noDeleteOnStaleGet: true }), 10)
+  const p2 = c.fetch(1)
+  c.set(1, 100)
+  t.equal(await p2, 10)
+  t.equal(c.get(1), 100)
 })
 
 t.test('background update on timeout, return stale', async t => {

tsconfig-base.json

@@ -9,7 +9,6 @@
     "isolatedModules": true,
     "moduleResolution": "node",
     "resolveJsonModule": true,
-    "skipLibCheck": true,
     "sourceMap": true,
     "inlineSources": true,
     "strict": true,