micropython/ports/webassembly/README.md

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MicroPython WebAssembly
=======================
MicroPython for [WebAssembly](https://webassembly.org/).
Dependencies
------------
Building webassembly port bears the same requirements as the standard
MicroPython ports with the addition of Emscripten (and uglify-js for the
minified file).
The output includes `micropython.js` (a JavaScript wrapper for the
MicroPython runtime) and `firmware.wasm` (actual MicroPython compiled to
WASM).
Build instructions
------------------
In order to build micropython.js, run:
$ make
To generate the minified file micropython.min.js, run:
$ make min
Running with Node.js
--------------------
Access the repl with:
$ node build/micropython.js
Stack size may be modified using:
$ node build/micropython.js -X stack=64K
Where stack size may be represented in Bytes, KiB or MiB.
MicroPython scripts may be executed using:
$ node build/micropython.js hello.py
Alternatively micropython.js may by accessed by other javascript programs in node
using the require command and the general API outlined below. For example:
```javascript
var mp_js = require('./build/micropython.js');
mp_js_init(64 * 1024);
mp_js_do_str("print('hello world')\n");
```
Running with HTML
-----------------
The prerequisite for browser operation of micropython.js is to listen to the
`micropython-print` event, which is passed data when MicroPython code prints
something to stdout. The following code demonstrates basic functionality:
```html
<!doctype html>
<html>
<head>
<script src="build/micropython.js"></script>
</head>
<body>
<pre id="micropython-stdout"></pre>
<script>
document.addEventListener("micropython-print", function(e) {
let output = document.getElementById("micropython-stdout");
output.innerText += new TextDecoder().decode(e.detail);
}, false);
var mp_js_startup = Module["onRuntimeInitialized"];
Module["onRuntimeInitialized"] = async function() {
mp_js_startup();
mp_js_init(64 * 1024);
mp_js_do_str("print('hello world')");
};
</script>
</body>
</html>
```
MicroPython code execution will suspend the browser so be sure to atomize usage
within this environment. Unfortunately interrupts have not been implemented for the
browser.
Testing
-------
Run the test suite using:
$ make test
API
---
The following functions have been exposed to javascript.
```
mp_js_init(stack_size)
```
Initialize MicroPython with the given stack size in bytes. This must be
called before attempting to interact with MicroPython.
```
mp_js_do_str(code)
```
Execute the input code. `code` must be a `string`.
```
mp_js_init_repl()
```
Initialize MicroPython repl. Must be called before entering characters into
the repl.
```
mp_js_process_char(char)
```
Input character into MicroPython repl. `char` must be of type `number`. This
will execute MicroPython code when necessary.