lazyThenable: revise comment & signerature

jokester · Apr 6, 2024 · 9139a3c · 9139a3c
1 parent b8dacf1
commit 9139a3c
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Showing 2 changed files with 7 additions and 5 deletions.
diff --git a/src/concurrency/lazy-thenable.spec.ts b/src/concurrency/lazy-thenable.spec.ts
@@ -13,12 +13,13 @@ describe(lazyThenable, () => {
     await wait(0);
     expect(called).toEqual(1);
     expect(await converted).toEqual(1);
+    expect(await lazy1).toEqual(1);
     expect(called).toEqual(1);
   });
 
   it('run actual action at most once', async () => {
     let called = 0;
-    const lazy2 = lazyThenable(async () => ++called);
+    const lazy2 = lazyThenable(() => ++called);
 
     expect(await lazy2).toEqual(1);
     for (let i = 0; i < 10; i++) {

diff --git a/src/concurrency/lazy-thenable.ts b/src/concurrency/lazy-thenable.ts
@@ -1,12 +1,13 @@
 /**
- * create a lazy, at-most-once PromiseLike from async function
+ * create a lazy PromiseLike to run {@name io} at most once and only after being awaited
  * @param io
+ * @return
  */
-export function lazyThenable<T>(io: () => PromiseLike<T>): PromiseLike<T> {
-  let r: null | Promise<T> = null;
+export function lazyThenable<T>(io: () => T): PromiseLike<Awaited<T>> {
+  let r: null | Promise<Awaited<T>> = null;
   return {
     then<TResult1, TResult2 = never>(
-      onfulfilled?: ((value: T) => PromiseLike<TResult1> | TResult1) | undefined | null,
+      onfulfilled?: ((value: Awaited<T>) => PromiseLike<TResult1> | TResult1) | undefined | null,
       onrejected?: ((reason: any) => PromiseLike<TResult2> | TResult2) | undefined | null,
     ): PromiseLike<TResult1 | TResult2> {
       return (r ??= Promise.resolve(io())).then(onfulfilled, onrejected);