1 files changed, 54 insertions, 0 deletions
diff --git a/app/assets/javascripts/lib/utils/ajax_cache.js b/app/assets/javascripts/lib/utils/ajax_cache.js
new file mode 100644
index 00000000000..cf030d613df
--- /dev/null
+++ b/app/assets/javascripts/lib/utils/ajax_cache.js
@@ -0,0 +1,54 @@
+class AjaxCache {
+  constructor() {
+    this.internalStorage = { };
+    this.pendingRequests = { };
+  }
+
+  get(endpoint) {
+    return this.internalStorage[endpoint];
+  }
+
+  hasData(endpoint) {
+    return Object.prototype.hasOwnProperty.call(this.internalStorage, endpoint);
+  }
+
+  remove(endpoint) {
+    delete this.internalStorage[endpoint];
+  }
+
+  retrieve(endpoint) {
+    if (this.hasData(endpoint)) {
+      return Promise.resolve(this.get(endpoint));
+    }
+
+    let pendingRequest = this.pendingRequests[endpoint];
+
+    if (!pendingRequest) {
+      pendingRequest = new Promise((resolve, reject) => {
+        // jQuery 2 is not Promises/A+ compatible (missing catch)
+        $.ajax(endpoint) // eslint-disable-line promise/catch-or-return
+        .then(data => resolve(data),
+          (jqXHR, textStatus, errorThrown) => {
+            const error = new Error(`${endpoint}: ${errorThrown}`);
+            error.textStatus = textStatus;
+            reject(error);
+          },
+        );
+      })
+      .then((data) => {
+        this.internalStorage[endpoint] = data;
+        delete this.pendingRequests[endpoint];
+      })
+      .catch((error) => {
+        delete this.pendingRequests[endpoint];
+        throw error;
+      });
+
+      this.pendingRequests[endpoint] = pendingRequest;
+    }
+
+    return pendingRequest.then(() => this.get(endpoint));
+  }
+}
+
+export default new AjaxCache();