feat: get.peek reads atom value without subscribing to updates

README.md

@@ -18,7 +18,7 @@ npm i jotai-effect
 type CleanupFn = () => void
 
 type EffectFn = (
-  get: Getter,
+  get: Getter & { peek: Getter },
   set: Setter & { recurse: Setter },
 ) => CleanupFn | void
 
@@ -107,6 +107,9 @@ function MyComponent() {
     set(countAtom, increment)
   })
   ```
+
+  </details>
+
 - **Supports Recursion:**
   Recursion is supported with `set.recurse` for both sync and async use cases, but is not supported in the cleanup function.
 
@@ -128,6 +131,23 @@ function MyComponent() {
 
   </details>
 
+- **Supports Peek:**
+  Read atom data without subscribing to changes with `get.peek`.
+
+  <!-- prettier-ignore -->
+  <details style="cursor: pointer; user-select: none;">
+    <summary>Example</summary>
+
+  ```js
+  const countAtom = atom(0)
+  atomEffect((get, set) => {
+    // will not rerun when countAtom changes
+    const count = get.peek(countAtom)
+  })
+  ```
+
+  </details>
+
 - **Executes In The Next Microtask:**
   `effectFn` runs in the next available microtask, after all Jotai synchronous read evaluations have completed.
 

src/atomEffect.ts

@@ -2,11 +2,11 @@ import type { Atom, Getter, Setter } from 'jotai/vanilla'
 import { atom } from 'jotai/vanilla'
 
 type CleanupFn = () => void
-
+type GetterWithPeek = Getter & { peek: Getter }
 type SetterWithRecurse = Setter & { recurse: Setter }
 
 export function atomEffect(
-  effectFn: (get: Getter, set: SetterWithRecurse) => void | CleanupFn
+  effectFn: (get: GetterWithPeek, set: SetterWithRecurse) => void | CleanupFn
 ) {
   const refAtom = atom(() => ({
     mounted: false,
@@ -17,6 +17,7 @@ export function atomEffect(
     recursing: false,
     refresh: () => {},
     refreshing: false,
+    get: (() => {}) as Getter,
     set: (() => {}) as Setter,
   }))
 
@@ -26,6 +27,7 @@ export function atomEffect(
     const ref = get(refAtom)
     ref.mounted = mounted
     if (mounted) {
+      ref.get = get
       ref.set = set
       ref.refresh = () => {
         try {
@@ -60,11 +62,14 @@ export function atomEffect(
       return ref.promise
     }
     const currDeps = new Map<Atom<unknown>, unknown>()
-    const getter: Getter = (a) => {
+    const getter: GetterWithPeek = (a) => {
       const value = get(a)
       currDeps.set(a, value)
       return value
     }
+    getter.peek = (anAtom) => {
+      return ref.get(anAtom)
+    }
     const setter: SetterWithRecurse = (...args) => {
       try {
         ++ref.inProgress