In JavaScript when accessing an attribute such as `obj.attr` a value of
`undefined` is returned if the attribute does not exist. This is unlike
Python semantics where an `AttributeError` is raised. Furthermore, in some
cases in JavaScript (eg a Proxy instance) `attr in obj` can return false
yet `obj.attr` is still valid and returns something other than `undefined`.
So the source of truth for whether a JavaScript attribute exists is to just
right away attempt `obj.attr`.
To more closely match these JavaScript semantics when proxying a JavaScript
object through to Python, change the attribute lookup logic on a `JsProxy`
so that it immediately attempts `obj.attr` instead of first testing if the
attribute exists via `attr in obj`.
This allows JavaScript objects which dynamically create attributes to work
correctly on the Python side, with both `obj.attr` and `obj["attr"]`. Note
that `obj["attr"]` already works in all cases because it immediately does
the subscript access without first testing if the attribute exists.
As a benefit, this new behaviour matches the Pyodide behaviour.
Signed-off-by: Damien George <damien@micropython.org>
And clear the corresponding `proxy_js_ref[js_ref]` entry when the finaliser
runs. This then allows the JavaScript side to (eventually) free the
corresponding JavaScript object.
Signed-off-by: Damien George <damien@micropython.org>
This commit adds a significant portion of the existing MicroPython asyncio
module to the webassembly port, using parts of the existing asyncio code
and some custom JavaScript parts.
The key difference to the standard asyncio is that this version uses the
JavaScript runtime to do the actual scheduling and waiting on events, eg
Promise fulfillment, timeouts, fetching URLs.
This implementation does not include asyncio.run(). Instead one just uses
asyncio.create_task(..) to start tasks and then returns to the JavaScript.
Then JavaScript will run the tasks.
The implementation here tries to reuse as much existing asyncio code as
possible, and gets all the semantics correct for things like cancellation
and asyncio.wait_for. An alternative approach would reimplement Task,
Event, etc using JavaScript Promise's. That approach is very difficult to
get right when trying to implement cancellation (because it's not possible
to cancel a JavaScript Promise).
Signed-off-by: Damien George <damien@micropython.org>
This optimises the case where a Python function is, for example, stored to
a JavaScript attribute and then later retrieved from Python. The Python
function no longer needs to be a proxy with double proxying needed for the
call from Python -> JavaScript -> Python.
Signed-off-by: Damien George <damien@micropython.org>
With this commit, `interpreter.runPythonAsync(code)` can now be used to run
Python code that uses `await` at the top level. That will yield up to
JavaScript and produce a thenable, which the JavaScript runtime can then
resume. Also implemented is the ability for Python code to await on
JavaScript promises/thenables. For example, outer JavaScript code can
await on `runPythonAsync(code)` which then runs Python code that does
`await js.fetch(url)`. The entire chain of calls will be suspended until
the fetch completes.
Signed-off-by: Damien George <damien@micropython.org>
This commit improves the webassembly port by adding:
- Proxying of Python objects to JavaScript with a PyProxy type that lives
on the JavaScript side. PyProxy implements JavaScript Proxy traps such
as has, get, set and ownKeys, to make Python objects have functionality
on the JavaScript side.
- Proxying of JavaScript objects to Python with a JsProxy type that lives
on the Python side. JsProxy passes through calls, attributes,
subscription and iteration from Python to JavaScript.
- A top-level API on the JavaScript side to construct a MicroPython
interpreter instance via `loadMicroPython()`. That function returns an
object that can be used to execute Python code, access the Python globals
dict, access the Emscripten filesystem, and other things. This API is
based on the API provided by Pyodide (https://pyodide.org/). As part of
this, the top-level file is changed from `micropython.js` to
`micropython.mjs`.
- A Python `js` module which can be used to access all JavaScript-side
symbols, for example the DOM when run within a browser.
- A Python `jsffi` module with various helper functions like
`create_proxy()` and `to_js()`.
- A dedenting lexer which automatically dedents Python source code if every
non-empty line in that source starts with a common whitespace prefix.
This is very helpful when Python source code is indented within a string
within HTML or JavaScript for formatting reasons.
Signed-off-by: Damien George <damien@micropython.org>
