feat: add support for shallow state merging

.changeset/spicy-monkeys-march.md

@@ -0,0 +1,5 @@
+---
+"zusdux": patch
+---
+
+Add support for shallow state merging

README.md

@@ -21,7 +21,9 @@ First, you create a store with the `createStore` function. It takes an object wi
 -   `initialState` - It's... well... the _initial state_ of your store
 
 -   `actions` - An object containing a list of actions that can be performed on the state. The actions can be either synchronous or asynchronous, they can take any
-    number of arguments, while the first one is a `set` function that allows you to update the store's state
+    number of arguments, while the first one is a `set` function that allows you to update the store's stat. The `set` function can accept either a new state object
+    that will be shallowly merged with the current state, or a function that receives the current state and returns the new state.
+    (See [Zustand](https://docs.pmnd.rs/zustand/guides/updating-state)'s documentation for more info)
 
 ```ts
 // store.ts
@@ -65,10 +67,7 @@ export const { actions, getState, setState, subscribe, useStore } = createStore(
 			},
 
 			setName: (set, firstName: string, lastName: string) => {
-				set((prev) => ({
-					...prev,
-					name: firstName + ' ' + lastName,
-				}));
+				set({ name: firstName + ' ' + lastName });
 			},
 		},
 	},

src/__tests__/index.test.ts

@@ -46,6 +46,15 @@ describe('Zusdux', () => {
 			name: 'counter',
 			count: 5,
 		});
+
+		// Act.
+		setState({ count: 10 });
+
+		// Assert.
+		expect(getState()).toStrictEqual({
+			name: 'counter',
+			count: 10,
+		});
 	});
 
 	it('should change the state using actions', () => {
@@ -222,7 +231,11 @@ describe('Zusdux', () => {
 		expectTypeOf(getState).toEqualTypeOf<() => ExpectedState>();
 
 		expectTypeOf(setState).toEqualTypeOf<
-			(setter: (prevState: ExpectedState) => ExpectedState) => void
+			(
+				setterOrState:
+					| ((prevState: ExpectedState) => ExpectedState)
+					| Partial<ExpectedState>,
+			) => void
 		>();
 
 		expectTypeOf(useStore).toEqualTypeOf<
@@ -259,10 +272,7 @@ function createCounter() {
 			},
 
 			setName: (set, firstName: string, lastName: string) => {
-				set((prev) => ({
-					...prev,
-					name: firstName + ' ' + lastName,
-				}));
+				set({ name: firstName + ' ' + lastName });
 			},
 		},
 	});

src/index.ts

@@ -22,8 +22,11 @@ export function createStore<
 
 	const getState = () => state;
 
-	const setState: SetState<S> = (setter) => {
-		state = setter(state);
+	const setState: SetState<S> = (setterOrState) => {
+		state =
+			typeof setterOrState === 'function'
+				? setterOrState(state)
+				: { ...state, ...setterOrState };
 
 		notify();
 	};

src/types.ts

@@ -9,4 +9,6 @@ export type ParseActions<
 		: never;
 };
 
-export type SetState<S> = (setter: (prevState: S) => S) => void;
+export type SetState<S> = (
+	setterOrState: ((prevState: S) => S) | Partial<S>,
+) => void;