feat(overmind): add WHEN utility

Author: christianalfoni

packages/node_modules/overmind/src/index.test.ts

@@ -29,6 +29,9 @@ function createDefaultOvermind() {
     await Promise.resolve()
     context.state.foo = 'bar2'
   }
+  const whenFooChanges: Action<void, Promise<void>> = async (context) => {
+    await context.when(() => context.state.foo === 'bar2')
+  }
   const changeValue: Action<{ isAwesome: boolean }> = (_, value) => {
     value.isAwesome = !value.isAwesome
   }
@@ -47,6 +50,7 @@ function createDefaultOvermind() {
     changeFooWithEffect,
     changeValue,
     waitAndChangeFoo,
+    whenFooChanges
   }
   const effects = {
     hello() {
@@ -357,6 +361,15 @@ describe('Overmind', () => {
     ).not.toThrow()
     expect(app.state.item.isAwesome).toBe(false)
   })
+  test('should allow waiting for mutation', async () => {
+    expect.assertions(1)
+    const app = createDefaultOvermind()
+    await Promise.all([
+      app.actions.whenFooChanges(),
+      app.actions.changeFoo()
+    ])
+    expect(app.state.foo).toBe('bar2')
+  })
 })
 
 describe('Overmind mock', () => {

packages/node_modules/overmind/src/index.ts

@@ -478,6 +478,16 @@ export class Overmind<ThisConfig extends IConfiguration>
       execution,
       proxyStateTree: this.proxyStateTree,
       effects: this.trackEffects(this.effects, execution),
+      when: (cb: () => boolean) => {
+        return new Promise((resolve) => {
+          const dispose = this.addFlushListener(() => {
+            if (cb()) {
+              dispose()
+              resolve()
+            }
+          })
+        })
+      },
       revertable: (cb: () => void) => {
         const mutations: IMutation[] = []
         const dispose = this.addMutationListener((mutation) => {

packages/node_modules/overmind/src/operator.ts

@@ -174,6 +174,7 @@ export function createOperator<ThisConfig extends IConfiguration>(
           actions: context.actions,
           execution: context.execution,
           revertable: context.revertable,
+          when: context.when
         },
         context.value,
         (err, value, options = {}) => {
@@ -276,6 +277,7 @@ export function createMutationOperator<ThisConfig extends IConfiguration>(
           actions: context.actions,
           execution: context.execution,
           revertable: context.revertable,
+          when: context.when
         },
         process.env.NODE_ENV === 'production'
           ? context.value

packages/node_modules/overmind/src/types.ts

@@ -37,6 +37,7 @@ export type IContext<ThisConfig extends IConfiguration> = {
   state: ResolveState<ThisConfig['state']>
   actions: ResolveActions<ThisConfig['actions']>
   effects: ThisConfig['effects']
+  when: (cb: () => boolean) => Promise<void>
   revertable: (mutationsCallback: () => any) => () => void
 }