check if atom has onMount property before queueing processOnMount callback

dmaskasky · dmaskasky · commit 474f5dabfd59 · 2026-04-01T13:04:40.000-07:00
diff --git a/src/vanilla/internals.ts b/src/vanilla/internals.ts
@@ -837,7 +837,7 @@ const BUILDING_BLOCK_mountAtom: MountAtom = (store, atom) => {
       t: new Set(),
     }
     mountedMap.set(atom, mounted)
-    if (isActuallyWritableAtom(atom)) {
+    if (isActuallyWritableAtom(atom) && atom.onMount) {
       const processOnMount = () => {
         let isSync = true
         const setAtom = (...args: unknown[]) => {

Original file line number	Diff line number	Diff line change
`@@ -837,7 +837,7 @@ const BUILDING_BLOCK_mountAtom: MountAtom = (store, atom) => {`
`837`	`837`	`t: new Set(),`
`838`	`838`	`}`
`839`	`839`	`mountedMap.set(atom, mounted)`
`840`		`- if (isActuallyWritableAtom(atom)) {`
	`840`	`+ if (isActuallyWritableAtom(atom) && atom.onMount) {`
`841`	`841`	`const processOnMount = () => {`
`842`	`842`	`let isSync = true`
`843`	`843`	`const setAtom = (...args: unknown[]) => {`