# Boxlang Runtime Wasm In The Browser
> Use this skill when compiling BoxLang to WebAssembly or JavaScript ES modules for use in web browsers and Node.js using MatchBox's --target js or --target wasm flags, integrating with HTML pages, bundlers (Webpack/Vite), and Node.js projects.
- Skill: `ortus-boxlang/boxlang-runtime-wasm-in-the-browser` (Agent Skill)
- Install (CLI): `npx skillmds@latest add ortus-boxlang/boxlang-runtime-wasm-in-the-browser`
- Raw SKILL.md: https://api.skillmd.com/api/skills/ortus-boxlang/boxlang-runtime-wasm-in-the-browser/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Web & Frontend
- Author: ortus-boxlang (https://skillmd.com/u/ortus-boxlang)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/ortus-boxlang/boxlang-runtime-wasm-in-the-browser
---
# BoxLang WASM in the Browser
## Overview
MatchBox can compile BoxLang source to browser-compatible output via two modes:
| Mode | Flag | Output | Best For |
|------|------|--------|---------|
| ES Module (recommended) | `--target js` | `.js` + `.wasm` | Browsers, Node.js, bundlers |
| Raw WASM | `--target wasm` | `.wasm` | Custom loaders, advanced bundling |
All top-level BoxLang functions are automatically exported, regardless of access modifier.
---
## Mode 1: `--target js` — ES Module (Recommended)
```bash
matchbox --target js my_lib.bxs
# Output: my_lib.js + my_lib.wasm
```
The generated `.js` file is an ES module wrapper. The `.wasm` file is loaded automatically.
### Browser Usage
```html
BoxLang in the Browser
```
### BoxLang source (`my_lib.bxs`)
```js
// All top-level functions are exported automatically
function greet( name ) {
return "Hello, " & name & "!"
}
function calculateTotal( prices ) {
return prices.reduce( ( sum, price ) -> sum + price, 0 )
}
```
### Node.js Usage
```js
// node-app.mjs
import { greet, calculateTotal } from './my_lib.js'
console.log( greet( "Node.js" ) )
console.log( calculateTotal([ 10.99, 5.49, 3.00 ]) )
```
```bash
node node-app.mjs
```
---
## Mode 2: `--target wasm` — Raw WASM
```bash
matchbox --target wasm my_lib.bxs
# Output: my_lib.wasm
```
Use this when you need manual control over WASM loading, or integration with Webpack/Vite:
```js
// Manual loading
const { instance } = await WebAssembly.instantiateStreaming(
fetch('/my_lib.wasm'),
{}
)
const { greet } = instance.exports
```
### Vite Integration
```js
// vite.config.js
import { defineConfig } from 'vite'
export default defineConfig({
assetsInclude: ['**/*.wasm'],
plugins: []
})
```
```js
// main.js — with Vite WASM handling
import wasmUrl from './my_lib.wasm?url'
const response = await fetch(wasmUrl)
const { instance } = await WebAssembly.instantiateStreaming(response)
const { greet } = instance.exports
```
---
## Function Export Rules
- **All top-level functions** are exported automatically (no `public` annotation needed)
- Functions defined inside class bodies are NOT exported
- Keep exported BoxLang functions at the top level of the `.bxs` file
```js
// ✅ Exported — top-level function
function add( a, b ) {
return a + b
}
// ✅ Exported — top-level function
function formatCurrency( amount, currency = "USD" ) {
return currency & " " & numberFormat( amount, "2" )
}
// ❌ NOT exported — inside a class
class MyLib {
function helper() { ... }
}
```
---
## Browser Compatibility
| Browser | ES Module WASM Support |
|---------|----------------------|
| Chrome 61+ | ✅ |
| Firefox 60+ | ✅ |
| Safari 14.1+ | ✅ |
| Edge 79+ | ✅ |
| Node.js 14+ | ✅ |
---
## Bundler Integration
### Webpack 5
```js
// webpack.config.js
module.exports = {
experiments: {
asyncWebAssembly: true
}
}
```
```js
// app.js
const myLib = await import('./my_lib.js')
myLib.greet("Webpack")
```
### Vite + ES Module
```bash
# Place my_lib.js + my_lib.wasm in /public or /src/assets
# Import as ES module (no special config needed for --target js output)
```
```js
import { greet } from '/my_lib.js'
greet("Vite")
```
---
## Development Workflow
```bash
# 1. Write BoxLang logic
cat > utils.bxs << 'EOF'
function slugify( text ) {
return text.lCase().reReplace( "[^a-z0-9]+", "-", "all" ).trim( "-" )
}
function truncate( text, maxLen = 100 ) {
return text.len() > maxLen ? text.left( maxLen ) & "..." : text
}
EOF
# 2. Compile to ES module
matchbox --target js utils.bxs
# 3. Serve (for browser testing — WASM requires HTTP, not file://)
npx serve .
# 4. Import in your app
```
> **Important:** WASM files must be served over HTTP (not `file://`). Use a local dev server like `npx serve`, Vite, or a browser extension during development.
---
## Checklist
- [ ] Use `--target js` for browser and Node.js integration (simpler than raw WASM)
- [ ] Keep exported functions at the top level of the `.bxs` file
- [ ] Serve via HTTP (not `file://`) — browsers block WASM from `file://` origins
- [ ] For bundlers (Vite/Webpack), copy both `.js` and `.wasm` output files together
- [ ] Use `--target wasm` only when you need manual loader control or advanced bundling
- [ ] Test in Node.js first for faster iteration before testing in the browser