feat(demo): hooks useRequest 异步数据管理 (#3447)

packages/hooks/src/useRequest/utils/subscribeFocus.ts

@@ -0,0 +1,30 @@
+import { isBrowser } from './isBrowser';
+import { isDocumentVisible } from './isDocumentVisible';
+import { isOnline } from './isOnline';
+
+type Listener = () => void;
+
+const listeners: Listener[] = [];
+
+if (isBrowser) {
+  const revalidate = () => {
+    if (!isDocumentVisible() || !isOnline()) return;
+    for (let i = 0; i < listeners.length; i++) {
+      const listener = listeners[i];
+      listener();
+    }
+  };
+  window.addEventListener('visibilitychange', revalidate, false);
+  window.addEventListener('focus', revalidate, false);
+}
+
+export default function subscribe(listener: Listener) {
+  listeners.push(listener);
+
+  return function unsubscribe() {
+    const index = listeners.indexOf(listener);
+    if (index > -1) {
+      listeners.splice(index, 1);
+    }
+  };
+}