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# Data prototypes

> **Studio writes this format for you.** The source editors in the Data panel ([Data sources](/docs/studio/logic/data-sources)) generate these entries field by field, and this page documents the underlying model.

A `$prototype` entry declares where a state value comes from instead of what it is. The prototype names a class, whether a built-in Web-API wrapper, a content loader, or your own, and the entry's remaining keys are its configuration. The resolved value is reactive: when the source changes, everything bound to it updates.

The smallest complete data prototype is an HTTP request whose URL tracks another state value:

```json shiki
```

## Built-in Web-API prototypes

These resolve automatically, with no imports or `$src`, and each maps to a genuine Web API:

- `Request`: HTTP fetch with reactive URL parameters, debouncing, and manual mode.
- `LocalStorage`: a persistent key-value entry that survives closing the browser.
- `SessionStorage`: the same, scoped to the visit.
- `Cookie`: a cookie with `maxAge`, `path`, `domain`, `secure`, and `sameSite`. Name it with the `__Host-` prefix and the rest is filled in for you: `Secure`, `Path=/`, and no `Domain`, which is what the browser requires of that name and refuses the cookie without. `SameSite: "none"` likewise implies `Secure`. There is no `expires`, because `maxAge` wins wherever both appear, and no `HttpOnly`, which a cookie written by the page could never read back.
- `IndexedDB`: a browser database store with indexes and CRUD helpers.
- `FormData`: form fields assembled for submission.
- `URLSearchParams`: a computed query string.
- `Set` / `Map`: reactive wrappers over the corresponding collections.
- `Blob`: binary data from parts and a MIME type.
- `Array`: a reactive array driving a [mapped list](/docs/framework/concepts/lists).

Field-level documentation for each source lives in [Data sources](/docs/studio/logic/data-sources). A storage entry is as small as:

```json shiki
```

## Content prototypes

Content loaders are built in too, and resolve at build time (`timing: "compiler"`; see [Timing](/docs/framework/concepts/timing)):

- `MarkdownFile`: parses one `.md` file into frontmatter and a content tree.
- `MarkdownCollection`: globs and parses many `.md` files.
- `ContentCollection`: a schema-validated, multi-format content source.
- `ContentEntry`: a single entry within a collection.

```json shiki
```

These names map internally to `.class.json` implementations shipped with Jx, with no configuration needed.

## External classes

Any other prototype name is an **external class**. Its `$src` must point to a `.class.json` file: a JSON Schema document describing the class's parameters, fields, and methods, optionally delegating to a JS module via `$implementation`:

```json shiki
```

The class contract is small: the constructor receives one configuration object (the entry minus reserved keys), and the value resolves through `instance.resolve()` (async), then `instance.value`, then the instance itself. A class may also expose `subscribe`/`unsubscribe` for push updates, and its methods may declare `returns` schemas so tooling knows, for example, that instances can feed mapped iteration. Authoring your own `.class.json` classes is covered in depth in the Extending section.

## Import maps

To avoid repeating `$src` on every entry, declare a top-level `imports` map from prototype names to `.class.json` paths:

```json shiki
```

`imports` in `site.json` cascade to every page; page-level entries win on collision, and an explicit `imports` entry may even override a built-in prototype mapping.

## How it works

The scope builder injects any import-mapped `$src`, constructs the class with the entry's configuration, and wraps the resolved value in a reactive reference automatically. Resolution order for `$src` is: explicit `$src` → page `imports` → site `imports` → built-in mappings → unknown-prototype warning. Configuration values that are `$ref`s are reactive, so a `Request` whose `urlParams` reference state re-fetches when that state changes. The `timing` field decides where resolution happens: in the browser, on the server, or at build time. See [Timing](/docs/framework/concepts/timing).

## Rules

- A non-Function `$src`**must** point to a `.class.json` file. Direct `.js` sources are for `$prototype: "Function"` only (see [Functions and sidecars](/docs/framework/concepts/functions)).
- Reserved keys (`$prototype`, `$src`, `$export`, `timing`, `default`, `description`) are never passed to the constructor.
- Import-map values must end in `.class.json`; anything else is warned about and skipped.
- An entry's own `$src` always beats the import map.
- Built-in prototypes need no `imports` entry and are unaffected by the map unless explicitly overridden.

## Related

- [Timing](/docs/framework/concepts/timing): client, server, and compiler resolution
- [State](/docs/framework/concepts/state): the grammar prototypes live inside
- [Lists](/docs/framework/concepts/lists): iterating over a source's resolved array
- [Reactivity](/docs/framework/concepts/reactivity): how resolved values propagate
- [Data sources in Studio](/docs/studio/logic/data-sources): every field, source by source
- [The Data panel in Studio](/docs/studio/logic/data): inspecting resolved values live

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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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