Preact: whole-file .mx (alpha)

A plain .mx file on the Preact host is the whole component. There is no function to write: MX emits the default-exported function component, and export interface Input becomes its props type.

Alpha. .preact.mx is the form to start with. Whole-file .mx suits a template with little logic of its own: it trades Preact’s function for MX’s statements, and hooks read less naturally there.

Counter.mx
import { useState } from "preact/hooks";

export interface Input {
  label: string;
}

<const/state=useState(0)/>
<const/count=state[0]/>
<const/setCount=state[1]/>

<button onClick() { setCount(count + 1); }>${input.label}: ${count}</button>
<if=(count > 2)><p>That is plenty.</p></if>
  • Props are input: input.label.
  • Hooks go in <const>, which becomes a statement in the component body. static is module scope and must not call a hook.
  • import, static and export are hoisted to the module.
  • Marko’s stateful tags are errors that name the hook to use: <let> names useState, <effect> names useEffect, <id> names useId.

Selecting the host

A whole-file .mx has no host in its name, so package.json says which one compiles it: "mx": { "host": "preact" }. A project whose only @mxlang/* host or target package is this one may leave the field out; with @mxlang/html installed too, say which. mx.target: "preact-jsx" selects Preact too; if both are given and disagree, the tools report target-host-mismatch.

Setup is the same as for region files. Everything in What MX compiles to applies; a whole-file template also has <const/x=expr/> (a const in the component body) and <return>.

examples/preact-app is a complete whole-file app.

Previous What MX compiles to Next Hono