webassembly: Implement runPythonAsync() for top-level async code.

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>

1 files changed, 10 insertions, 0 deletions

diff --git a/ports/webassembly/api.js b/ports/webassembly/api.js
index dfe756176..ec0601c61 100644
--- a/ports/webassembly/api.js
+++ b/ports/webassembly/api.js
@@ -140,6 +140,16 @@ export async function loadMicroPython(options) {
             );
             return proxy_convert_mp_to_js_obj_jsside_with_free(value);
         },
+        runPythonAsync(code) {
+            const value = Module._malloc(3 * 4);
+            Module.ccall(
+                "mp_js_do_exec_async",
+                "number",
+                ["string", "pointer"],
+                [code, value],
+            );
+            return proxy_convert_mp_to_js_obj_jsside_with_free(value);
+        },
     };
 }