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# Statements

> **Studio writes this format for you.** The statement editor ([Statements](/docs/studio/logic/statements)) builds these bodies as visual step cards, and this page documents the JSON those cards write to disk.

A [Function entry](/docs/framework/concepts/functions)'s `body` may be a **JSON array of statements** instead of a JavaScript source string. Each statement is one step; steps run top to bottom, exactly like the statement list inside a JavaScript function, but as structure, so tooling can validate, inspect, and edit every step.

The smallest complete structured body mutates, then notifies:

```json shiki
```

There are six statement kinds, each reusing a web-platform name:

| Kind       | Shape                                                     | Source of the name                   |
| ---------- | --------------------------------------------------------- | ------------------------------------ |
| Expression | a bare expression node (mutation or `call`)               | ECMAScript ExpressionStatement       |
| Branch     | `{ "if", "then", "else"? }`                               | JSON Schema conditional keywords     |
| Multiway   | `{ "$switch", "cases", "default"? }`                      | Element-level `$switch`, ECMA switch |
| Dispatch   | `{ "dispatchEvent", "detail"?, "bubbles"?, "composed"? }` | WHATWG DOM `dispatchEvent`           |
| Stop       | `{ "stopPropagation": true }`                             | WHATWG DOM `stopPropagation()`       |
| Cancel     | `{ "preventDefault": true }`                              | WHATWG DOM `preventDefault()`        |

## Expression statements

Any mutating [expression node](/docs/framework/concepts/expressions), or a `call`, stands alone as a step. No wrapper key; the node appears bare in the array:

```json shiki
```

To capture a result, make the step an assignment whose `value` is a `call` node. There is no dedicated capture field:

```json shiki
```

## Branches

`if` holds a **pure** expression operand; `then` and `else` hold statement lists. `else` is optional:

```json shiki
```

## Multiway branches

`$switch` mirrors the element-level [`$switch`](/docs/framework/concepts/switching) in statement position: the discriminant is a pure operand, `cases` maps its **string form** to statement lists, and the optional `default` runs when no key matches:

```json shiki
```

## Dispatching events

`dispatchEvent` fires a DOM `CustomEvent`, and the statement's other keys mirror `CustomEventInit`. `detail` may be a literal, a `$ref`, or an expression node:

```json shiki
```

The event dispatches from the handler's `event.currentTarget` (or the component instance in compiled custom elements). Declare the events a function fires in its `emits` array so Studio can autocomplete them.

## Stopping and cancelling events

`stopPropagation` and `preventDefault` act on the event the handler is running for. Each is written as the member set to `true`, so the step reads as the call it becomes:

```json shiki
```

Stop the event when an ancestor handles the same one and must not see this occurrence: a row nested inside another row, a button inside a clickable card. Cancel the default when the element's built-in behaviour is not wanted: a link that opens in place, a form the body submits itself, an arrow key that would otherwise scroll. Outside a handler, where there is no event, both steps do nothing.

## Parameters

A structured body follows the named-formula pattern. Without `parameters`, the entry is an event handler, and statements see `state` and the `event#/` scheme. With `parameters`, it is a callable invoked positionally, its arguments bound to `$args/` names:

```json shiki
```

## Statements, expressions, or a body string?

The escalation ladder continues inside Shape 4. Prefer the least powerful form:

| Form                          | Use when                                                                          |
| ----------------------------- | --------------------------------------------------------------------------------- |
| A single `$expression`        | One operation: toggle, increment, push, a computed value                          |
| `body` as a statement array   | Multiple steps, branching, or dispatching events, still with no code              |
| `body` as a JavaScript string | Loops, `await` chains, try/catch, browser APIs: anything statements can't express |

A statement body stays fully analyzable and visually editable; a source string is opaque to tooling. Reach for the string only when structure genuinely runs out.

## How it works

One engine serves both halves: an interpreter (`runStatements`) executes statement arrays directly against the reactive `state` proxy, and a compiler (`compileStatements`) emits the genuine ECMAScript forms: `if`/`else` statements, a `switch` over the discriminant's string form, `dispatchEvent(new CustomEvent(type, init))`, and `event.stopPropagation()` / `event.preventDefault()`. The emitted function is identical in shape to a hand-written handler, so [reactivity](/docs/framework/concepts/reactivity) tracking works unchanged.

Statements execute sequentially. A step whose value is a promise is awaited before the next step runs, giving async/await semantics without writing `await`.

## Rules

- A `body` is either a statement array or a source string, one representation per entry.
- Branch tests (`if`) and `$switch` discriminants are **pure** operands: no mutations, no `call` to a mutating entry.
- `$switch` matches `String(discriminant)` against `cases` keys, because JSON keys are strings.
- Statements run in order; thenable results are awaited before the next step.
- There is no capture field; assign a `call`'s result with an `=` statement.
- `dispatchEvent` needs a dispatch target; outside a handler (no `event`), a compiled custom element dispatches from the component instance.
- Declare dispatched events in `emits`, which is the declaration tooling reads.
- `stopPropagation` and `preventDefault` need the handler's event; outside a handler they do nothing.

## Related

- [Expressions](/docs/framework/concepts/expressions): the nodes statements are built from
- [Functions and sidecars](/docs/framework/concepts/functions): the entries that own a `body`
- [Switching](/docs/framework/concepts/switching): `$switch` at the element level
- [Statements in Studio](/docs/studio/logic/statements): the visual step editor
- [Code editing in Studio](/docs/studio/logic/code): the JavaScript escape hatch

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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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