onmount

Onmount is a term used in frontend development to denote a lifecycle hook or event that fires after a component's DOM elements have been inserted into the document. It is typically used to perform operations that require the element to exist in the DOM, such as measuring layout, initializing third‑party libraries, or fetching initial data.

In practice, the exact name and mechanism vary by framework. Some ecosystems provide a dedicated onmount or mounted hook, while others use a generic effect or lifecycle method. The hook generally runs only on the client, not during server-side rendering, because it relies on the DOM APIs.

Usage patterns include setting up event listeners, starting data fetches, or manipulating DOM nodes directly. It is common to pair onmount with a cleanup step that runs when the component is removed from the DOM to avoid leaks.

Examples in common tools include: in Svelte, onMount(() => { /* … */ }); in Vue 3's composition API, onMounted(() => { /* … */ }); In React, the closest analogue is useEffect with an empty dependency array.

Related concepts include lifecycle hooks, onunmount or destroyed hooks, and other mounting phases across different frameworks. Because naming and semantics differ, developers should consult the specific framework documentation for exact behavior.