replace 'undefined' with 'void 0'

.changeset/curvy-countries-flow.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: replace `undefined` with `void 0` to avoid edge case

packages/svelte/src/compiler/phases/3-transform/client/visitors/VariableDeclaration.js

@@ -117,7 +117,7 @@ export function VariableDeclaration(node, context) {
 
 			const args = /** @type {CallExpression} */ (init).arguments;
 			const value =
-				args.length === 0 ? b.id('undefined') : /** @type {Expression} */ (context.visit(args[0]));
+				args.length === 0 ? b.unary('void', b.literal(0)) : /** @type {Expression} */ (context.visit(args[0]));
 
 			if (rune === '$state' || rune === '$state.raw') {
 				/**

packages/svelte/src/compiler/phases/3-transform/server/visitors/CallExpression.js

@@ -13,7 +13,7 @@ export function CallExpression(node, context) {
 	const rune = get_rune(node, context.state.scope);
 
 	if (rune === '$host') {
-		return b.id('undefined');
+		return b.unary('void', b.literal(0));
 	}
 
 	if (rune === '$effect.tracking') {

packages/svelte/src/compiler/phases/3-transform/server/visitors/VariableDeclaration.js

@@ -45,7 +45,7 @@ export function VariableDeclaration(node, context) {
 						) {
 							const right = node.right.arguments.length
 								? /** @type {Expression} */ (context.visit(node.right.arguments[0]))
-								: b.id('undefined');
+								: b.unary('void', b.literal(0));
 							return b.assignment_pattern(node.left, right);
 						}
 					}
@@ -76,7 +76,7 @@ export function VariableDeclaration(node, context) {
 
 			const args = /** @type {CallExpression} */ (init).arguments;
 			const value =
-				args.length === 0 ? b.id('undefined') : /** @type {Expression} */ (context.visit(args[0]));
+				args.length === 0 ? b.unary('void', b.literal(0)) : /** @type {Expression} */ (context.visit(args[0]));
 
 			if (rune === '$derived.by') {
 				declarations.push(