From fd023fbff2fabc73d04d12fca8b071ff3c4fd519 Mon Sep 17 00:00:00 2001
From: paoloricciuti <ricciutipaolo@gmail.com>
Date: Thu, 22 Jan 2026 16:26:25 +0100
Subject: [PATCH] feat: add `beforeMount` callback to `MountOptions`

---
 .changeset/cyan-kings-wait.md                 | 5 +++++
 packages/svelte/src/index.d.ts                | 4 ++++
 packages/svelte/src/internal/client/render.js | 7 ++++++-
 3 files changed, 15 insertions(+), 1 deletion(-)
 create mode 100644 .changeset/cyan-kings-wait.md

diff --git a/.changeset/cyan-kings-wait.md b/.changeset/cyan-kings-wait.md
new file mode 100644
index 0000000000..8381b6305c
--- /dev/null
+++ b/.changeset/cyan-kings-wait.md
@@ -0,0 +1,5 @@
+---
+'svelte': minor
+---
+
+feat: add `beforeMount` callback to `MountOptions`
diff --git a/packages/svelte/src/index.d.ts b/packages/svelte/src/index.d.ts
index a1782f5b61..7fd64c15c8 100644
--- a/packages/svelte/src/index.d.ts
+++ b/packages/svelte/src/index.d.ts
@@ -333,6 +333,10 @@ export type MountOptions<Props extends Record<string, any> = Record<string, any>
 	 * Can be accessed via `getContext()` at the component level.
 	 */
 	context?: Map<any, any>;
+	/**
+	 * A function invoked before the component is mounted but after the component context has been initialized.
+	 */
+	beforeMount?: () => void;
 	/**
 	 * Whether or not to play transitions on initial render.
 	 * @default true
diff --git a/packages/svelte/src/internal/client/render.js b/packages/svelte/src/internal/client/render.js
index c76f0b1ce7..6d7046a111 100644
--- a/packages/svelte/src/internal/client/render.js
+++ b/packages/svelte/src/internal/client/render.js
@@ -158,7 +158,10 @@ const document_listeners = new Map();
  * @param {MountOptions} options
  * @returns {Exports}
  */
-function _mount(Component, { target, anchor, props = {}, events, context, intro = true }) {
+function _mount(
+	Component,
+	{ target, anchor, props = {}, beforeMount, events, context, intro = true }
+) {
 	init_operations();
 
 	/** @type {Set<string>} */
@@ -214,6 +217,8 @@ function _mount(Component, { target, anchor, props = {}, events, context, intro
 					ctx.c = context;
 				}
 
+				beforeMount?.();
+
 				if (events) {
 					// We can't spread the object or else we'd lose the state proxy stuff, if it is one
 					/** @type {any} */ (props).$$events = events;