micropython/ports/javascript/README.md

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MicroPython.js
==============
MicroPython transmuted into Javascript by Emscripten.
Dependencies
------------
Building micropython.js bears the same requirements as the standard MicroPython
ports with the addition of Emscripten (and uglify-js for the minified file).
A standard installation of Emscripten should provide functional code, however
if memory errors are encountered it may be worthwhile to modify the tool.
`emscripten-fastcomp/lib/Target/JSBackend.cpp` may require the minor fix
found in JSBackend.patch. This patch attempts to address situations where
C code running through Emscripten is denied access to Javascript variables
leading to false-positives in the MicroPython garbage collector as variables
with pointers exclusively in Javascript will be erased prematurely.
Refer to Emscripten documentation for instructions on building Emscripten
from source.
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 an element with
the id `mp_js_stdout` which receives `print` events. The following code
demonstrates basic functionality:
```html
<!doctype html>
<html>
<head>
<script src="build/micropython.js"></script>
</head>
<body>
<div id='mp_js_stdout'></div>
<script>
mp_js_stdout.addEventListener('print', function(e) {
document.write(e.data);
}, false);
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.