[Skip to content](#main-content) [![Jx Suite](/favicon.svg) Suite](/)Search⌘KESC Jump to [Install Jx Studio](/docs/start/install)[Build your first project](/docs/start/first-project)[Document format](/docs/framework/concepts/documents)[Formula catalog](/docs/framework/reference/formulas) ↵ select↑↓ navigateesc close [Studio](/studio)[Framework](/framework)[Templates](/templates)[Compare](/compare)[Docs](/docs/start/first-project)[GitHub](https://github.com/jxsuite/jx)[Download](/download) ✕ [Studio](/studio)[Framework](/framework)[Templates](/templates)[Compare](/compare)[Docs](/docs/start/first-project)[GitHub](https://github.com/jxsuite/jx) Color scheme [Download](/download) ☰ Docs menu 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 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formats](/docs/extending/extensions/formats/)[Capability methods](/docs/extending/extensions/capabilities/)[Project sections](/docs/extending/extensions/project-sections/)[Server mounts](/docs/extending/extensions/server/)[Connectors](/docs/extending/extensions/connectors/)[Search indexes](/docs/extending/extensions/search/)[Security and secrets](/docs/extending/extensions/security/)[Tutorial: a TOML format](/docs/extending/extensions/tutorial-toml-format/)[Tutorial: a guestbook](/docs/extending/extensions/tutorial-guestbook/)[First-party extensions](/docs/extending/extensions/first-party/)Embedding[Overview](/docs/extending/embedding/)[Hosting the Studio assets](/docs/extending/embedding/hosting/)[Writing a platform adapter](/docs/extending/embedding/platform-adapter/)[The backend protocol](/docs/extending/embedding/backend-protocol/)[Dev server internals](/docs/extending/embedding/dev-server/)[Embedding the runtime in your app](/docs/extending/embedding/runtime-host/)[Writing assistant tools](/docs/extending/embedding/assistant-harness/)UI kit[The Jx UI kit](/docs/extending/ui-kit/)Reference[Protocol routes](/docs/extending/reference/studio-routes/)[Implementation status](/docs/extending/reference/implementation-status/)[Spec changelog](/docs/extending/reference/spec-changelog/)[Standards alignment](/docs/extending/reference/standards/)Contributing[Working in the monorepo](/docs/extending/contributing/monorepo/)[Contributing to these docs](/docs/extending/contributing/docs/)[AI assistant evals](/docs/extending/contributing/ai-evals/) # Components > **Studio writes this format for you.** This page documents the underlying JSON, which is useful when you want to hand-edit a file, review a diff, or understand what the visual tools produce. A Jx component is a single `.json` file. All state, computed values, and functions are declared in `state`. Simple components need no sidecar file. ## A component is one file ```json shiki ``` ## The four shapes of a state entry Every entry in `state` is one of four shapes, and you can tell which by looking at it. Nothing declares the shape; the entry's own structure decides. ### Shape 1: a naked value A JSON scalar, array, or plain object with no reserved keys: ```json shiki ``` ### Shape 2: a typed value An object with a `default` property and optional `type`: ```json shiki ``` ### Shape 3: a computed template string A string containing ${} syntax: ```json shiki ``` A string that is one ${} from end to end keeps the expression's own value, so `isEmpty` is a real boolean; any text around it makes the value a string. See [State](/docs/framework/concepts/state#shape-3-computed-templates). ### Shape 4: a prototype (`$prototype`) An object with `$prototype` for functions and data sources: ```json shiki ``` ## External sidecars When functions grow complex, extract them to a `.js` file: ```json shiki ``` ```js shiki ``` The first parameter is always `state`, the component's reactive scope. `this` is never used. ## Custom elements A component whose `tagName` contains a hyphen is a custom element: ```json shiki ``` Custom elements render to the **light DOM**. Nothing attaches a shadow root, so scoping is done with selectors instead: a component's own rules are prefixed with its tag name, and a nested element with its own `style` gets a generated `.-` class. ```css shiki ``` Note This cuts both ways. Your page CSS **can** reach into a component and restyle it, which is handy when you want it and the reason a stray global rule can change a component you didn't touch. There is no encapsulation boundary to stop either one. **Handlers written at the root listen on the element itself.** An `onclick`, `onkeydown` or `ontoggle` beside `tagName` attaches to the host, with the component's own `state` and the host as `event.currentTarget`. That is where a component's contract belongs: a row's activation or a panel's keyboard handling arrives at the element, not at a wrapper it had to render to hear it. ```json shiki ``` ## Opting into a shadow root If you want that boundary, ask for it per component: ```json shiki ``` Or for the whole project, with `"defaults": { "shadow": "open" }` in `project.json`. A component's own `$shadow` always wins, including `"$shadow": false`, which is how you keep one component in the light DOM when everything else moved. The build emits a **declarative shadow root**, so the component paints correctly before any JavaScript runs: ```html shiki ``` ### What changes | | Light DOM (default) | `$shadow` | | ------------------------- | --------------------------------------- | ---------------------- | | Page CSS reaches in | yes | no | | `` | emulated: children are moved into place | real slot distribution | | Your styles are scoped by | the tag name | `:host` | | Stylesheet lives in | the page `` | the shadow root | **Slots are the difference that matters.** The light-DOM emulation *moves* your children into the component's rendered tree. A real slot leaves them where they are and projects them, so they stay your page's children, your page's CSS still styles them, and the component reaches them with `::slotted()`. Tip Write `:host` in your styles either way. In a shadow component it stays `:host` ; in a light one the build turns it into the tag name, and `:host(.wide)` into `sd-card.wide` . That means the same style object works in both modes, so flipping `$shadow` doesn't silently break your CSS. `closed` works too, and means what the standard says: nothing outside can reach the root, not even your own scripts via `element.shadowRoot`. Use it when you mean it. ## Props and encapsulation Props are passed via `$props` on an instance node, which is the only mechanism for crossing component boundaries. Register the component in `$elements` and instantiate it by its custom-element tag: ```json shiki ``` Signal scope is bounded at the component level. No implicit scope leaking. An instance can sit inside another component's own `children` as well as on a page or in a slot, and the build expands it at every level, props resolved against the enclosing component's state. See [Components inside components](/docs/framework/build#components-inside-components) for what the compiler writes and the one shape it refuses (a component that renders itself with the same props). The live runtime refuses that shape too, with the same words. A component that instantiates its own tag inside its own `children`, forwarding the same props, is stopped at the level where the props repeat: that instance stays an empty element, the console reports `Component renders itself: my-card → my-card …`, and the rest of the page, its siblings and every other `` included, renders as usual. The refused element also dispatches a bubbling `jx-error` event (an `ErrorEvent`, with the diagnostic as its `error` and `message`), so a page can listen for the refusal where a console line is out of reach. A component that renders itself with props that change at each level (a tree node) is allowed up to 32 levels deep in the runtime as in the build; past that it is reported the same way, with the chain it walked. Slot content does not count: `` written on a page is two instances, not a component rendering itself. One shape only the runtime can meet, a component whose `onMount` or a later state change flips a `$switch` into its own tag again, is ended by the same 32-level cap rather than by the cycle check, because at that point the runtime cannot tell a component looping from a user opening one more level of a tree. ## When a component cannot render yet A component whose render throws with the values it was given (a card that formats an empty `date` with `Intl/formatDate`, say) is reported the same way: `Jx: was not rendered:` in the console and a `jx-error` event from the element, with the rest of the page drawn around it. In the live runtime that is not final. A prop bound to data that arrives later, such as a collection the page loads after its first render, reaches the component after it connected, so when one of the component's props changes the runtime draws it again, and its `onMount` runs once a render succeeds. The same error is reported once, not on every attempt. `onMount` receives the component's state and the element, and runs with the element as `this`, as a built site runs it. A prop named like a property every element has, such as `title` or `lang`, reaches the component from a parent's `$props` even when it changes after the component connected. ✕ 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 Access](/docs/studio/interface/quick-access/)[Keyboard shortcuts](/docs/studio/interface/shortcuts/)[Preferences](/docs/studio/interface/preferences/)[Languages](/docs/studio/interface/languages/)[Problems and progress](/docs/studio/interface/problems-and-progress/)[Commands](/docs/studio/interface/commands/)Projects[Overview](/docs/studio/projects/)[Create a project](/docs/studio/projects/create/)[Pages, layouts, components](/docs/studio/projects/pages-layouts-components/)[The Content workspace](/docs/studio/projects/browse/)[Starter templates](/docs/studio/projects/starters/)[Media](/docs/studio/projects/media/)[Content types](/docs/studio/projects/content-types/)[Project settings](/docs/studio/projects/settings/)[Dependencies and imports](/docs/studio/projects/dependencies/)Edit mode[Overview](/docs/studio/editing/)[Writing and 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sources](/docs/studio/logic/data-sources/)[Code editing](/docs/studio/logic/code/)Databases[Overview](/docs/studio/data/)[Connections](/docs/studio/data/connections/)[Data tables](/docs/studio/data/tables/)[Data grid](/docs/studio/data/grid/)[Auth and secrets](/docs/studio/data/auth-and-secrets/)AI assistant[Overview](/docs/studio/ai/)[The AI assistant](/docs/studio/ai/chat/)[Document assistant](/docs/studio/ai/document-assistant/)Publish[Overview](/docs/studio/publish/)[Source control](/docs/studio/publish/source-control/)[GitHub](/docs/studio/publish/github/)[Cloudflare Pages](/docs/studio/publish/cloudflare/)[Other hosts](/docs/studio/publish/other-hosts/)[Redirects](/docs/studio/publish/redirects/)[Real-time collaboration](/docs/studio/publish/collaboration/)Framework[Overview](/docs/framework/)Concepts[Documents](/docs/framework/concepts/documents/)[Elements](/docs/framework/concepts/elements/)[Components](/docs/framework/concepts/components/)[Props and 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architecture[Overview](/docs/framework/site/)[project.json](/docs/framework/site/project-json/)[Routing](/docs/framework/site/routing/)[Layouts](/docs/framework/site/layouts/)[Content collections](/docs/framework/site/content-collections/)[Jx Markdown](/docs/framework/site/jx-markdown/)[Obsidian vault as content](/docs/framework/site/obsidian-vault/)[Relationships](/docs/framework/site/relationships/)[SEO and metadata](/docs/framework/site/seo/)[Locales and languages](/docs/framework/site/i18n/)[Images](/docs/framework/site/images/)[Redirects](/docs/framework/site/redirects/)[Feeds](/docs/framework/site/feeds/)[Site search](/docs/framework/site/search/)[Build output and adapters](/docs/framework/site/deployment/)How compilation works[Overview](/docs/framework/build/)[The dev server](/docs/framework/build/dev-server/)[CLI commands](/docs/framework/build/cli/)Working with agents[Overview](/docs/framework/agents/)[Authoring rules for 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guestbook](/docs/extending/extensions/tutorial-guestbook/)[First-party extensions](/docs/extending/extensions/first-party/)Embedding[Overview](/docs/extending/embedding/)[Hosting the Studio assets](/docs/extending/embedding/hosting/)[Writing a platform adapter](/docs/extending/embedding/platform-adapter/)[The backend protocol](/docs/extending/embedding/backend-protocol/)[Dev server internals](/docs/extending/embedding/dev-server/)[Embedding the runtime in your app](/docs/extending/embedding/runtime-host/)[Writing assistant tools](/docs/extending/embedding/assistant-harness/)UI kit[The Jx UI kit](/docs/extending/ui-kit/)Reference[Protocol routes](/docs/extending/reference/studio-routes/)[Implementation status](/docs/extending/reference/implementation-status/)[Spec changelog](/docs/extending/reference/spec-changelog/)[Standards alignment](/docs/extending/reference/standards/)Contributing[Working in the monorepo](/docs/extending/contributing/monorepo/)[Contributing to these 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