[minor] allow for infinite staleness (#28)

* [minor] allow for infinite staleness * Update index.js * Update README.md Co-authored-by: Jacob Page <[email protected]> * Update lib/multi-level.js Co-authored-by: Jacob Page <[email protected]> * Update multi-level.js * Update multi-level.js Co-authored-by: Jacob Page <[email protected]>
godaddy · Jan 10, 2022 · 4bd3d47 · 4bd3d47
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diff --git a/README.md b/README.md
@@ -22,8 +22,8 @@ You can instantiate the cache with 3 configurable options: `maxAge`,
 `maxStaleness`, and `fsCachePath`.
 
 - `maxAge`: The duration, in milliseconds, before a cached item expires
-- `maxStaleness`: The duration, in milliseconds, in which expired cache
-items are still served
+- `maxStaleness`: (Optional) The duration, in milliseconds, in which expired cache
+items are still served. Defaults to 0, meaning never serve data past expiration. Can also be set to `Infinity`, meaning always give at least a cached version.
 - `fsCachePath`: (Optional) file path to create a file-system based cache
 - `shouldCache`: (Optional) a function to determine whether or not you will
 cache a found item

diff --git a/lib/multi-level.js b/lib/multi-level.js
@@ -36,7 +36,7 @@ function getValue(opts, key, defaultValue) {
  *
  * @param {Object} opts Options for the Client instance
  * @param {Number} [opts.maxAge=600000] The duration, in milliseconds, before a cached item expires (defaults to 600,000)
- * @param {Number} [opts.maxStaleness=0] The duration, in milliseconds, in which expired cache items are still served
+ * @param {Number} [opts.maxStaleness=0] The duration, in milliseconds, in which expired cache items are still served. Supports Infinity.
  * @param {ShouldCache} [opts.shouldCache=()=>true] Function to determine whether to not we should cache the result
  * @param {Cache[]}  opts.caches An Array of cache objects. See `./fs` and `./memory` for sample caches.
  */

diff --git a/test/index.test.js b/test/index.test.js
@@ -122,6 +122,17 @@ describe('Out of Band cache', () => {
       assume(expired.value).to.equal('milk');
     });
 
+    it('refreshes on an expired item, but returns stale if infinite staleness', async function () {
+      const fridge = new Cache({ maxAge: -10, maxStaleness: Infinity }); // items are immediately stale
+
+      await fridge.get('old milk', {}, async () => 'milk');
+      await sleep(100);
+      const expired = await fridge.get('old milk', { }, async () => { throw new Error('gross'); });
+
+      assume(expired.fromCache).is.truthy();
+      assume(expired.value).to.equal('milk');
+    });
+
     it('can override the cache-level maxStaleness', async function () {
       const fridge = new Cache({ maxAge: -10, maxStaleness: -10 }); // items are immediately stale