Cache electrum address history fetch a couple of seconds to prevent double requests on address page load.

backend/src/api/memory-cache.ts

@@ -0,0 +1,38 @@
+interface ICache {
+  type: string;
+  id: string;
+  expires: Date;
+  data: any;
+}
+
+class MemoryCache {
+  private cache: ICache[] = [];
+  constructor() {
+    setInterval(this.cleanup.bind(this), 1000);
+  }
+
+  public set(type: string, id: string, data: any, secondsExpiry: number) {
+    const expiry = new Date();
+    expiry.setSeconds(expiry.getSeconds() + secondsExpiry);
+    this.cache.push({
+      type: type,
+      id: id,
+      data: data,
+      expires: expiry,
+    });
+  }
+
+  public get<T>(type: string, id: string): T | null {
+    const found = this.cache.find((cache) => cache.type === type && cache.id === id);
+    if (found) {
+      return found.data;
+    }
+    return null;
+  }
+
+  private cleanup() {
+    this.cache = this.cache.filter((cache) => cache.expires < (new Date()));
+  }
+}
+
+export default new MemoryCache();