MendixWidgetGleam

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Build Mendix Pluggable Widgets with Gleam — no JSX required.

Write React components entirely in Gleam and run them as Mendix Studio Pro widgets. React bindings are provided by redraw/redraw_dom, Mendix API bindings by mendraw, and build tools + JS interop by glendix.

Why Gleam?

• Static type safety — Gleam's robust type system catches runtime errors at compile time
• Immutable data — Predictable state management
• JavaScript target support — gleam build --target javascript outputs ES modules
• glendix + mendraw packages — Type-safe Gleam bindings for React + Mendix API + JS Interop, supporting EditableValue, ActionValue, ListValue and all other Mendix Pluggable Widget API types

Architecture

src/
  mendix_widget_gleam.gleam           # Main widget module
  editor_config.gleam                 # Studio Pro property panel configuration
  editor_preview.gleam                # Studio Pro design view preview
  components/
    hello_world.gleam               # Shared Hello World component
  MendixWidget.xml                    # Widget property definitions
  package.xml                         # Mendix package manifest
package.json                            # npm dependencies (React, external libraries, etc.)
gleam.toml                            # Includes glendix >= 4.0.3 + mendraw dependency

React/Mendix FFI and JS Interop bindings are not included in this project — they are provided by the glendix and mendraw Hex packages.

Build Pipeline

Widget code (.gleam) + glendix package (Hex)
    |  gleam run -m glendix/build (Gleam compilation runs automatically)
ES modules (.mjs) — build/dev/javascript/...
    |  Bridge JS (auto-generated) handles imports
    |  Rollup (pluggable-widgets-tools)
.mpk widget package — dist/

Core Principles

The Gleam function fn(JsProps) -> Element has an identical signature to a React functional component. React bindings are provided by redraw / redraw_dom, while mendraw provides Mendix runtime type accessors and glendix provides JS interop, so widget projects need only focus on business logic.

// src/mendix_widget_gleam.gleam
import mendraw/mendix.{type JsProps}
import redraw.{type Element}
import redraw/dom/attribute
import redraw/dom/html

pub fn widget(props: JsProps) -> Element {
  let sample_text = mendix.get_string_prop(props, "sampleText")
  html.div([attribute.class("widget-hello-world")], [
    html.text("Hello " <> sample_text),
  ])
}

Mendix complex types can also be used in a type-safe manner from Gleam:

import mendraw/mendix
import mendraw/mendix/editable_value
import mendraw/mendix/action

pub fn widget(props: JsProps) -> Element {
  // Access EditableValue
  let name_attr: EditableValue = mendix.get_prop_required(props, "name")
  let display = editable_value.display_value(name_attr)

  // Execute ActionValue
  let on_save: Option(ActionValue) = mendix.get_prop(props, "onSave")
  action.execute_action(on_save)
  // ...
}

Getting Started

Prerequisites

• Gleam (v1.0+)
• Node.js (v16+)
• Mendix Studio Pro (for widget testing)

Installation

gleam run -m glendix/install   # Auto-downloads Gleam deps + installs npm deps + generates binding code (external React packages must be installed manually beforehand)

Build

gleam run -m glendix/build     # Gleam compilation + widget build (.mpk output)

Build artefacts are output as .mpk files in the dist/ directory.

Development

gleam run -m glendix/dev       # Gleam compilation + dev server (HMR, port 3000)
gleam run -m glendix/start     # Linked development with Mendix test project

Commands

All commands are unified under gleam. gleam run -m automatically compiles Gleam before running the script.

Command	Description
gleam run -m glendix/install	Install dependencies (Gleam + npm) + generate binding code
gleam run -m glendix/build	Production build (.mpk output)
gleam run -m glendix/dev	Development server (HMR, port 3000)
gleam run -m glendix/start	Linked development with Mendix test project
gleam run -m glendix/lint	Run ESLint
gleam run -m glendix/lint_fix	ESLint auto-fix
gleam run -m glendix/release	Release build
gleam run -m mendraw/marketplace	Search/download Mendix Marketplace widgets
gleam run -m glendix/define	Widget property definition TUI editor
gleam build --target javascript	Gleam to JS compilation only
gleam test	Run Gleam tests
gleam format	Format Gleam code

Using External React Components

React component libraries distributed as npm packages can be used from pure Gleam without writing any .mjs FFI files.

Step 1: Install the npm package

npm install recharts

Step 2: Add bindings to gleam.toml

Add a [tools.glendix.bindings] section to your gleam.toml:

[tools.glendix.bindings.recharts]
components = ["PieChart", "Pie", "Cell", "Tooltip", "ResponsiveContainer"]

Step 3: Generate bindings

gleam run -m glendix/install

A binding_ffi.mjs file is generated automatically. It is also regenerated on subsequent builds via gleam run -m glendix/build.

Step 4: Use from Gleam

import glendix/binding
import mendraw/interop
import redraw.{type Element}
import redraw/dom/attribute.{type Attribute}

fn m() { binding.module("recharts") }

pub fn pie_chart(attrs: List(Attribute), children: List(Element)) -> Element {
  interop.component_el(binding.resolve(m(), "PieChart"), attrs, children)
}

pub fn tooltip(attrs: List(Attribute)) -> Element {
  interop.void_component_el(binding.resolve(m(), "Tooltip"), attrs)
}

External React components follow the same calling pattern as html.div.

Tech Stack

• Gleam — Widget logic and UI (compiled to JavaScript target)
• glendix — Build tools + JS Interop Gleam bindings (Hex package)
• mendraw — Mendix API Gleam bindings (Hex package)
• React 19 — Mendix Pluggable Widget runtime
• Rollup — Bundling via @mendix/pluggable-widgets-tools

Limitations

• The Gleam to JS to Mendix Widget pipeline is not an officially supported combination; build configuration customisation may be required
• JSX files are not used — all React logic is implemented via Gleam + glendix
• React bindings use redraw/redraw_dom via glendix — other Gleam React libraries are not used
• FFI files are not written directly in the widget project — React/Mendix FFI is provided by glendix

Licence

Apache License 2.0 — see LICENSE