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# Lists and iteration

> **Studio writes this format for you.** Converting an element with **Repeat…** and binding its data source ([Repeaters](/docs/studio/design/repeaters)) writes the Array pseudo-elements on this page.

A dynamic list is an **Array pseudo-element**: an object with `$prototype: "Array"` sitting inside a `children` array. It names the data (`items`) and a template (`map`) rendered once per item. The list re-renders automatically whenever the data changes.

```json shiki
```

## The iteration context

Inside the `map` template, the `$map/`[reference scheme](/docs/framework/concepts/references) reads the current iteration:

| Reference                  | Resolves to                          |
| -------------------------- | ------------------------------------ |
| `{ "$ref": "$map/item" }`  | The current array item               |
| `{ "$ref": "$map/index" }` | The current zero-based integer index |

Deeper paths reach into item fields, as in `"$map/item/title"`, and template strings inside the template can read the same context as ${$map.item.title} or ${$map.index}:

```json shiki
```

The `map` template is an ordinary element def, so `attributes`, `id`, `className`, `style`, and event handlers all work there and can read the iteration context, which is how a list row gets a per-item link or a selected state:

```json shiki
```

## Mixing with sibling elements

The Array object is a *member* of `children`, so it can sit among ordinary siblings, such as a static header row followed by a dynamic list. It renders **wrapper-less**: mapped items become direct children of the parent element, with no container in between.

```json shiki
```

## Reading the row from a handler

One handler serves every row. Which row invoked it is on state as `state.$map`, with `item` and `index`:

```json shiki
```

This works on the map body and on any descendant of it. A nested list shadows the outer context for handlers inside it.

## Passing a row to a component

`$props` on the map body hands each item's data to a component. Template values are bindings, so they read the current row:

```json shiki
```

## Setting a property on each row

Properties that live on the DOM element rather than in markup (`value`, `checked`, `selected`, `disabled`) go directly on the map body, the same as anywhere else. They may interpolate `$map`:

```json shiki
```

Each `<option>` gets its row's `id` as its value, so a `change` handler reads the key rather than the label shown on screen. Put it in `attributes` instead and you get an HTML attribute, which for `value` sets only the *default*, and the two diverge as soon as the user interacts.

## Filtering and sorting

`filter` and `sort` reference [functions](/docs/framework/concepts/functions) declared in `state`. The filter function receives each item and returns true to keep it; the sort function receives two items and returns a number, like a standard comparator:

```json&#x20;shiki
```

Filtering and sorting never mutate the source array; they shape what renders.

## Keeping rows across changes

Give the list a `key` when people interact with its rows. The key is a `$map/item` pointer that names what makes each row itself.

```json&#x20;shiki
```

A keyed row keeps its element when the list changes. Reordering moves the element, inserting creates only the new rows, and removing tears down only the removed ones. Focus, scroll position, an open `<details>` and a half-typed value all survive. The `$map.index` of a row that moved updates in place.

Use `{ "$ref": "$map/item" }` to key by the item itself, which works for objects and for primitive values. A key that is missing on an item falls back to that item's position, and the runtime warns once. Two rows with the same key also warn once; the second and later rows are rebuilt on every change.

Without a key, rows are matched by position. That is fine for a list that only grows at the end, and wrong for one that reorders or inserts in the middle, because the element at each position is reused for whatever item lands there.

## How it works

The runtime places an invisible anchor where the Array object sits, then renders the mapped items inline ahead of it. The whole render runs inside a reactive effect: when `items` (or a filter or sort dependency) changes, the previous generation of item nodes and their bindings is disposed and the list re-renders in place. Each item's template renders in a child scope carrying `$map`, and the surrounding document's `state` remains fully visible inside the template.

## Rules

- The Array object must have `$prototype: "Array"`, an `items` source, and a `map` template.
- `items` must resolve to an array: a state entry, a [data prototype](/docs/framework/concepts/data-prototypes) such as a content collection, or a literal array.
- The list renders wrapper-less; give structure a container by making the *parent* the container element (`ul`, `tbody`, a grid `div`).
- `$map/` references are valid only inside the `map` template.
- `filter` and `sort` must be `$ref`s to functions in `state`.
- The legacy form where `children` is *itself* the Array object is still accepted; Studio normalizes it to a single array member on load.

## Related

- [References](/docs/framework/concepts/references): the `$map/` scheme and resolution order
- [State](/docs/framework/concepts/state): declaring the arrays lists iterate
- [Data prototypes](/docs/framework/concepts/data-prototypes): collections and requests as `items` sources
- [Content collections](/docs/framework/site/content-collections): site content as list data
- [Repeaters](/docs/studio/design/repeaters): the Studio surface that writes this format

✕

Start here[Overview](/docs/start/)Get started[Install Jx Studio](/docs/start/install/)[Your first project](/docs/start/first-project/)[A tour of Jx Studio](/docs/start/studio-tour/)Tutorials[Tutorial: interactive component](/docs/start/first-component/)[Tutorial: blog with collections](/docs/start/first-collection/)[Video tutorials](/docs/start/videos/)Coming from another tool[Coming from WordPress](/docs/start/coming-from-wordpress/)[Coming from Webflow or Framer](/docs/start/coming-from-webflow/)[Coming from Wix or Squarespace](/docs/start/coming-from-wix/)[Coming from Lovable or Builder.io](/docs/start/coming-from-ai-builders/)Studio[Overview](/docs/studio/)[The desktop app](/docs/studio/desktop/)The workspace[Overview](/docs/studio/interface/)[Welcome screen](/docs/studio/interface/welcome-screen/)[Editors and views](/docs/studio/interface/modes/)[The canvas](/docs/studio/interface/canvas/)[Documents and panes](/docs/studio/interface/tabs/)[Quick 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