fix: Make types of asyncComputed describe the value for pending more …

…accurately

packages/mobx-utils/index.d.ts

@@ -1,17 +1,17 @@
 import { IComputedValue } from 'mobx';
 
-export type IAsyncComputed<T> = {
-  value: IComputedValue<T>;
+export type IAsyncComputed<TValue, TPending> = {
+  value: IComputedValue<TValue | TPending>;
   pending: IComputedValue<boolean>;
   invalidate: () => void;
 };
 
-type AsyncComputedParams<T> = {
-  getValueFromObservedPromise: () => Promise<T>;
-  valueWhenPending?: T;
+type AsyncComputedParams<TValue, TPending> = {
+  getValueFromObservedPromise: () => Promise<TValue>;
+  valueWhenPending?: TValue | TPending;
   betweenUpdates?: 'show-pending-value' | 'show-latest-value';
 };
 
-export function asyncComputed<T>(
-  configuration: AsyncComputedParams<T>,
-): IAsyncComputed<T>;
+export function asyncComputed<TValue, TPending = undefined>(
+  configuration: AsyncComputedParams<TValue, TPending>,
+): IAsyncComputed<TValue, TPending>;

packages/mobx-utils/index.test-d.ts

@@ -0,0 +1,53 @@
+import { expectType } from 'tsd';
+import { asyncComputed } from './index';
+import { IComputedValue } from 'mobx';
+
+// asyncComputed, given showing latest value and specified pending value, typing is ok.
+const instance1 = asyncComputed({
+  getValueFromObservedPromise: () => Promise.resolve('some-value'),
+  valueWhenPending: 42,
+  betweenUpdates: 'show-latest-value',
+});
+
+expectType<{
+  value: IComputedValue<string | number>;
+  invalidate: () => void;
+  pending: IComputedValue<boolean>;
+}>(instance1);
+
+// asyncComputed, given showing latest value but no specified pending value, typing is ok.
+const instance2 = asyncComputed({
+  getValueFromObservedPromise: () => Promise.resolve('some-value'),
+  betweenUpdates: 'show-latest-value',
+});
+
+expectType<{
+  value: IComputedValue<string | undefined>;
+  invalidate: () => void;
+  pending: IComputedValue<boolean>;
+}>(instance2);
+
+// asyncComputed, given showing pending value between updates and specified pending value, typing is ok.
+const instance3 = asyncComputed({
+  getValueFromObservedPromise: () => Promise.resolve('some-value'),
+  valueWhenPending: 'some-initial-value',
+  betweenUpdates: 'show-pending-value',
+});
+
+expectType<{
+  value: IComputedValue<string>;
+  invalidate: () => void;
+  pending: IComputedValue<boolean>;
+}>(instance3);
+
+// asyncComputed, given showing pending value between updates, but no specified pending value, typing is ok.
+const instance4 = asyncComputed({
+  getValueFromObservedPromise: () => Promise.resolve('some-value'),
+  betweenUpdates: 'show-pending-value',
+});
+
+expectType<{
+  value: IComputedValue<string | undefined>;
+  invalidate: () => void;
+  pending: IComputedValue<boolean>;
+}>(instance4);

packages/mobx-utils/package.json

@@ -37,6 +37,7 @@
   "scripts": {
     "build": "ogre-tools-build-js",
     "test": "ogre-tools-test",
+    "test:types": "tsd",
     "code-style:verify": "ogre-tools-verify-code-style",
     "code-style:fix": "ogre-tools-fix-code-style"
   },