npm install @solid-primitives/lifecycle
yarn add @solid-primitives/lifecycle
pnpm add @solid-primitives/lifecycle


Package providing extra layer of lifecycle primitives for Solid.

  • createIsMounted - Returns a boolean signal indicating whether the component is mounted or not.
  • isHydrated - A signal with the same behavior as isHydrating but this one focused only on client-side updates.
  • onElementConnect - Calls the given callback when the target element is connected to the DOM.


Returns a boolean signal indicating whether the component is mounted or not.

It's a simple wrapper around createSignal and onMount, but it can make your code feel more declarative - especially when used with createMemo.

import { createIsMounted } from "@solid-primitives/lifecycle";

const isMounted = createIsMounted();
const windowWidth = createMemo(() => (isMounted() ? ref.offsetWidth : 0));

let ref: HTMLElement;
<div ref={ref}>{windowWidth()}</div>;


A signal accessor indicating if the owner is done hydrating.

  • false during SSR (always)
  • false on the client if the component evaluation is during a hydration process.
  • true on the client if the component evaluates after hydration or during clinet-side rendering.

If it returns true it means that you can safely change the initial values of signals that are used in the JSX, without causing a mismatch between the server and client.

It can be used in computations as a signal, and it will trigger a re-evaluation when the hydration state changes.

But it can also be used as a simple check of the hydration state.

import { isHydrated } from "@solid-primitives/lifecycle";

const serverFallback = 0;

const [vw, setVw] = createSignal(
  // if the component is hydrated, we can safely use the window width immediately
  isHydrated() ? window.innerWidth / 100 : serverFallback,

<p>Window width: {vw()}vw</p>;

#Implementing ClientOnly component

isHydrated can be used to easily implement a ClientOnly component that will only render its children on the client.

import { createMemo, FlowComponent, JSX } from "solid-js";
import { isHydrated } from "@solid-primitives/lifecycle";

// This component will only render its children on the client
export const ClientOnly: FlowComponent = props => {
  const children = createMemo(() => isHydrated() && props.children);
  return <>{children()}</>;

// Usage
  <ComponentThatBreaksOnServer />


onMount is a common lifecycle hook that is used to perform side-effects when the component is mounted. However, it is not certain that the elements are actually connected to the DOM when the mount callback is called.

Note If that's the case, it might be a sign that you are executing components that are not visible to the users my mistake.

And if this is something intentional, you probably already have a way to hook into the actual DOM rendering.

If you are not sure, you can use onElementConnect instead of onMount to make sure that you are caling your callback when the elements are connected to the DOM.

  ref={el => {
    // often false, but will be true during hydration

    onMount(() => {
      // often true, but will be false if the executed component is not actually getting rendered

    onElementConnect(el, () => {
      // always true


Live Site

You can see the primitives in action in the following sandbox: