1 files changed, 30 insertions, 0 deletions
diff --git a/src/lib/oncePromise.ts b/src/lib/oncePromise.ts
new file mode 100644
index 0000000..f6ce775
--- /dev/null
+++ b/src/lib/oncePromise.ts
@@ -0,0 +1,30 @@
+const ensurePromise = <T>(maybePromise: T | PromiseLike<T>): Promise<T> =>
+  typeof maybePromise === 'object' &&
+  maybePromise !== null &&
+  'then' in maybePromise &&
+  typeof maybePromise.then === 'function' &&
+  'catch' in maybePromise &&
+  typeof maybePromise.catch === 'function' &&
+  'finally' in maybePromise &&
+  typeof maybePromise.finally === 'function'
+    ? (maybePromise as Promise<T>)
+    : Promise.resolve(maybePromise);
+/** Returns a function that caches successful promises until time runs out, and throws away unsuccessful ones */
+export const oncePromise = <T>(create: () => Promise<T>, timeout = -1) => {
+  let getPromise = (): Promise<T> => {
+    const oldGetPromise = getPromise,
+      promise = ensurePromise(create()).catch((e) => {
+        getPromise = oldGetPromise;
+        throw e;
+      }),
+      expires = timeout > 0 ? performance.now() + timeout : 0;
+    return (getPromise = expires
+      ? ((() =>
+          performance.now() > expires
+            ? oldGetPromise()
+            : promise) as () => Promise<T>)
+      : () => promise)();
+  };
+  return () => getPromise();
+};
+export default oncePromise;