--- title: Imperative component API --- better title needed? - mount - unmount - render - hydrate - how they interact with each other Every Svelte application starts by imperatively creating a root component. On the client this component is mounted to a specific element. On the server, you want to get back a string of HTML instead which you can render. The following functions help you achieve those tasks. ## `mount` Instantiates a component and mounts it to the given target: ```js // @errors: 2322 import { mount } from 'svelte'; import App from './App.svelte'; const app = mount(App, { target: document.querySelector('#app'), props: { some: 'property' } }); ``` You can mount multiple components per page, and you can also mount from within your application, for example when creating a tooltip component and attaching it to the hovered element. Note that unlike calling `new App(...)` in Svelte 4, things like effects (including `onMount` callbacks, and action functions) will not run during `mount`. If you need to force pending effects to run (in the context of a test, for example) you can do so with `flushSync()`. ## `unmount` Unmounts a component created with [`mount`](#mount) or [`hydrate`](#hydrate): ```js // @errors: 1109 import { mount, unmount } from 'svelte'; import App from './App.svelte'; const app = mount(App, {...}); // later unmount(app); ``` ## `render` Only available on the server and when compiling with the `server` option. Takes a component and returns an object with `body` and `head` properties on it, which you can use to populate the HTML when server-rendering your app: ```js // @errors: 2724 2305 2307 import { render } from 'svelte/server'; import App from './App.svelte'; const result = render(App, { props: { some: 'property' } }); result.body; // HTML for somewhere in this tag result.head; // HTML for somewhere in this tag ``` ## `hydrate` Like `mount`, but will reuse up any HTML rendered by Svelte's SSR output (from the [`render`](#render) function) inside the target and make it interactive: ```js // @errors: 2322 import { hydrate } from 'svelte'; import App from './App.svelte'; const app = hydrate(App, { target: document.querySelector('#app'), props: { some: 'property' } }); ``` As with `mount`, effects will not run during `hydrate` — use `flushSync()` immediately afterwards if you need them to.