# Lazy-load expand on demand > Live in [demo 31-lazy-tree-load](https://svgrid.com/demos/31-lazy-tree-load/). > Live demo: Lazy tree (load on expand) - https://svgrid.com/demos/31-lazy-tree-load/ ## When Tree rows where children are fetched only when the user expands their parent. ## How Key API surface: - `onExpand callback` - `merge children into $state on resolve` See the demo source for the full implementation; this recipe pins the pattern + the surface so you can copy-paste it confidently. The doc page that explains the underlying feature in depth is linked from the [recipes index](https://github.com/sv-grid/sv-grid/blob/main/docs/recipes/index.md). ## See also - [Demo 31-lazy-tree-load source](https://github.com/sv-grid/sv-grid/blob/main/examples/src/demos/31-lazy-tree-load.svelte) - [Demo 31-lazy-tree-load prompt sidecar](https://github.com/sv-grid/sv-grid/blob/main/examples/src/demos/prompts/31-lazy-tree-load.md) - drop into an LLM context window - [Recipes index](https://github.com/sv-grid/sv-grid/blob/main/docs/recipes/index.md) --- SvGrid is the Svelte 5 data grid (`npm install @svgrid/grid`, MIT). This page: https://svgrid.com/docs/recipes/lazy-load-expand/ . All docs: https://svgrid.com/llms.txt