mx-undefined — Undefined Name

Severity: error | Blocks morph build: yes

What this error means

You reference a name that is not declared, imported, a component, or a supported native global:

error : mx-undefined : `cout` is not defined here and not imported
  hint: Did you mean `count`?
  Learn more: https://morph.levizr.com/docs/errors/mx-undefined

Lowercase JSX tags (<div>) and type positions (x: number) are excluded — only real value references are checked, with full scope awareness (shadowing, params, and imports all count as declared).

Why Morph raises it

Every identifier in .mx code must lower to something: a local, a prop, an import, a Morph API, or a supported runtime global (fetch, console, setTimeout, ...). An unresolved name has no lowering — the C++ backend would hit an undeclared identifier. Failing here gives you the file, line, column, and a Did you mean ... ? suggestion instead of a page of C++ errors.

Example that triggers it

import { morphState } from 'morph';

export default function App() {
  const [count, setCount] = morphState(0);
  // ❌ `cout` is a typo for `count` — mx-undefined
  return <div>{cout}</div>;
}

Other common causes:

• Missing import (Hero used but never imported — though capitalized tags usually surface as mx-component-unknown first).
• Using a variable outside its scope (inside a different component or block).
• Browser globals (document, localStorage) — those surface as mx-js-global, not here.

How to fix

import { morphState } from 'morph';

export default function App() {
  const [count, setCount] = morphState(0);
  // ✅ Reference the declared name
  return <div>{count}</div>;
}

Steps:

1. Read the suggestion — for typos it is usually exact.
2. If the name lives in another file, import it (components, helpers, stores).
3. If it is a Morph API, import it from 'morph' — see mx-no-morph-import.
4. If it is a browser/Node global, replace it with a Morph-native equivalent — see mx-js-global.
5. Re-run morph check.

Tuning this rule

Do not disable this rule. Unresolved names can never compile.

See also

• mx-no-morph-import — the name is a Morph API
• mx-component-unknown — the name is a component tag
• mx-js-global — the name is a browser global