`onMount`

Runs once when the component initializes. Signal accesses inside are not tracked.

import { onMount } from '@barefootjs/dom'

onMount(fn: () => void): void

#Basic Usage

onMount(() => {
  console.log('Component initialized')
})

Unlike createEffect, this function never re-runs. It executes once at initialization time.

#Common Patterns

#Reading browser state

onMount(() => {
  const hash = window.location.hash
  setFilter(hash === '#/active' ? 'active' : 'all')
})

#Setting up event listeners

onMount(() => {
  const handleHashChange = () => setFilter(getFilterFromHash())
  window.addEventListener('hashchange', handleHashChange)
  onCleanup(() => window.removeEventListener('hashchange', handleHashChange))
})

#Focusing an element

onMount(() => {
  inputElement.focus()
})

#How It Works

onMount is equivalent to:

createEffect(() => untrack(fn))

The function runs inside an effect context (so onCleanup works), but untrack prevents any signal reads from being tracked as dependencies.

#`onMount` vs `createEffect`

	onMount	createEffect
Runs on init	Yes	Yes
Re-runs on signal change	No	Yes
Tracks dependencies	No	Yes
Supports onCleanup	Yes	Yes