fix: use get in constructor for deriveds (#15300)

paoloricciuti · Rich-Harris · web-flow · commit ade66c6feade · 2025-03-21T15:21:40.000+01:00
Co-authored-by: Rich Harris &lt;rich.harris@vercel.com&gt;
diff --git a/.changeset/new-cherries-leave.md b/.changeset/new-cherries-leave.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: use `get` in constructor for deriveds
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/MemberExpression.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/MemberExpression.js
@@ -11,7 +11,9 @@ export function MemberExpression(node, context) {
 	if (node.property.type === 'PrivateIdentifier') {
 		const field = context.state.private_state.get(node.property.name);
 		if (field) {
-			return context.state.in_constructor ? b.member(node, 'v') : b.call('$.get', node);
+			return context.state.in_constructor && (field.kind === 'raw_state' || field.kind === 'state')
+				? b.member(node, 'v')
+				: b.call('$.get', node);
 		}
 	}
 
diff --git a/packages/svelte/tests/runtime-runes/samples/deriveds-in-constructor/_config.js b/packages/svelte/tests/runtime-runes/samples/deriveds-in-constructor/_config.js
@@ -0,0 +1,5 @@
+import { test } from '../../test';
+
+export default test({
+	html: `<p>state,derived state,derived.by derived state</p>`
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/deriveds-in-constructor/main.svelte b/packages/svelte/tests/runtime-runes/samples/deriveds-in-constructor/main.svelte
@@ -0,0 +1,18 @@
+<script>
+	class Foo {
+		#state = $state('state')
+		#derived = $derived('derived ' + this.#state);
+		#derivedBy = $derived.by(() => {
+			return 'derived.by ' + this.#derived 
+		});
+		
+		initial
+		
+		constructor() {
+			this.initial = [this.#state, this.#derived, this.#derivedBy]
+		}
+	}
+	const foo = new Foo()
+</script>
+
+<p>{foo.initial}</p>

-Original file line number
+Diff line change
@@ @@ -0,0 +1,5 @@ @@
 +---
 +'svelte': patch
 +---
++
 +fix: use `get` in constructor for deriveds
Original file line number	Diff line number	Diff line change
`@@ -11,7 +11,9 @@ export function MemberExpression(node, context) {`
`11`	`11`	`if (node.property.type === 'PrivateIdentifier') {`
`12`	`12`	`const field = context.state.private_state.get(node.property.name);`
`13`	`13`	`if (field) {`
`14`		`- return context.state.in_constructor ? b.member(node, 'v') : b.call('$.get', node);`
	`14`	`+ return context.state.in_constructor && (field.kind === 'raw_state' \|\| field.kind === 'state')`
	`15`	`+ ? b.member(node, 'v')`
	`16`	`+ : b.call('$.get', node);`
`15`	`17`	`}`
`16`	`18`	`}`
`17`	`19`