cached_resource.js

+import moment from "moment/moment";
+
+//
+
+class CachedResource {
+    constructor(
+        cachedResourceKey,
+        cachedTimestampKey,
+        source,
+        dirtyFunc,
+        refreshFunc,
+    ) {
+        this.cachedResourceKey = cachedResourceKey;
+        this.cachedTimestampKey = cachedTimestampKey;
+        this.dirtyFunc = dirtyFunc;
+        this.refreshFunc = refreshFunc;
+        // must have get/set methods
+        this.source = source;
+    }
+
+    async getOrRefresh() {
+        // assume the cache is dirty
+        let isDirty = true;
+        let resource = this.source.get(this.cachedResourceKey);
+        const cachedLastUpdated = this.source.get(this.cachedTimestampKey);
+        const lastUpdatedResponse = await this.dirtyFunc().catch(console.error);
+        const lastUpdated = lastUpdatedResponse.data;
+
+        // compare 'cheap' API result based on timestamp
+        if (resource) {
+            isDirty = moment(lastUpdated['timestamp']).isAfter(moment(cachedLastUpdated));
+        }
+
+        // refresh if anything has changed
+        if (isDirty) {
+            const resourceResponse = await this.refreshFunc().catch(console.error);
+            resource = resourceResponse.data;
+            this.source.set(this.cachedResourceKey, resource);
+            this.source.set(this.cachedTimestampKey, lastUpdated['timestamp']);
+            return resource;
+        } else {
+            return resource;
+        }
+    }
+}
+
+
+export {CachedResource};