diff --git a/.changeset/clean-dogs-launch.md b/.changeset/clean-dogs-launch.md
new file mode 100644
index 00000000000..0a3027e0dd0
--- /dev/null
+++ b/.changeset/clean-dogs-launch.md
@@ -0,0 +1,8 @@
+---
+"@gradio/core": patch
+"@self/app": patch
+"@self/spa": patch
+"gradio": patch
+---
+
+fix: Execute function strings passed to `Blocks.launch(js=...)`
diff --git a/js/app/src/routes/[...catchall]/+page.svelte b/js/app/src/routes/[...catchall]/+page.svelte
index 45b3b977868..de0a74a8995 100644
--- a/js/app/src/routes/[...catchall]/+page.svelte
+++ b/js/app/src/routes/[...catchall]/+page.svelte
@@ -301,16 +301,6 @@
 
 		await add_custom_html_head(config.head);
 
-		if (config.js) {
-			try {
-				const script = document.createElement("script");
-				script.textContent = config.js;
-				document.head.appendChild(script);
-			} catch (e) {
-				console.error("Error executing custom JS:", e);
-			}
-		}
-
 		dispatch("loaded");
 		if (config.dev_mode) {
 			setTimeout(() => {
diff --git a/js/core/src/Blocks.svelte b/js/core/src/Blocks.svelte
index 4fc4faf66b0..e144dbe88a7 100644
--- a/js/core/src/Blocks.svelte
+++ b/js/core/src/Blocks.svelte
@@ -17,6 +17,7 @@
 
 	import MountComponents from "./MountComponents.svelte";
 	import { prefix_css } from "./css";
+	import { execute_custom_js } from "./custom_js";
 	import { reactive_formatter } from "./gradio_helper";
 
 	import logo from "./images/logo.svg";
@@ -467,7 +468,15 @@
 		});
 		res.observe(root_container);
 
-		app_tree.ready.then(() => {
+		app_tree.ready.then(async () => {
+			if (js) {
+				try {
+					await execute_custom_js(js);
+				} catch (e) {
+					console.error("Error executing custom JS:", e);
+				}
+			}
+
 			ready = true;
 			dep_manager.dispatch_load_events();
 		});
diff --git a/js/core/src/custom_js.test.ts b/js/core/src/custom_js.test.ts
new file mode 100644
index 00000000000..c177375a1b8
--- /dev/null
+++ b/js/core/src/custom_js.test.ts
@@ -0,0 +1,36 @@
+import { afterEach, describe, expect, test } from "vitest";
+import { execute_custom_js } from "./custom_js";
+
+declare global {
+	var custom_js_result: string | undefined;
+}
+
+afterEach(() => {
+	delete globalThis.custom_js_result;
+});
+
+describe("execute_custom_js", () => {
+	test("invokes a function expression", async () => {
+		await execute_custom_js(
+			"() => { globalThis.custom_js_result = 'function'; }"
+		);
+
+		expect(globalThis.custom_js_result).toBe("function");
+	});
+
+	test("awaits an async function expression", async () => {
+		await execute_custom_js(
+			"async () => { await Promise.resolve(); globalThis.custom_js_result = 'async'; }"
+		);
+
+		expect(globalThis.custom_js_result).toBe("async");
+	});
+
+	test("executes raw JavaScript", async () => {
+		await execute_custom_js(
+			"const result = 'raw'; globalThis.custom_js_result = result;"
+		);
+
+		expect(globalThis.custom_js_result).toBe("raw");
+	});
+});
diff --git a/js/core/src/custom_js.ts b/js/core/src/custom_js.ts
new file mode 100644
index 00000000000..ee13723ce0b
--- /dev/null
+++ b/js/core/src/custom_js.ts
@@ -0,0 +1,16 @@
+import { AsyncFunction } from "./init_utils";
+
+export async function execute_custom_js(js: string): Promise<void> {
+	let custom_js: () => Promise<unknown>;
+
+	try {
+		custom_js = new AsyncFunction(`return (${js});`);
+	} catch {
+		custom_js = new AsyncFunction(js);
+	}
+
+	const result = await custom_js();
+	if (typeof result === "function") {
+		await result();
+	}
+}
diff --git a/js/spa/src/Index.svelte b/js/spa/src/Index.svelte
index c1c31398ffe..da27ed69d99 100644
--- a/js/spa/src/Index.svelte
+++ b/js/spa/src/Index.svelte
@@ -387,15 +387,6 @@
 		if (config.deep_link_state === "invalid") {
 			pending_deep_link_error = true;
 		}
-		if (config.js) {
-			try {
-				const script = document.createElement("script");
-				script.textContent = config.js;
-				document.head.appendChild(script);
-			} catch (e) {
-				console.error("Error executing custom JS:", e);
-			}
-		}
 		if (config.dev_mode) {
 			setTimeout(() => {
 				const { host } = new URL(api_url);