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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>
35 lines
801 B
JavaScript
35 lines
801 B
JavaScript
// Test lookup of attributes on JsProxy objects.
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const mp = await (await import(process.argv[2])).loadMicroPython();
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// Simple attribute names and values.
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globalThis.obj1 = { a: 1, b: 2 };
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// Unconventional attribute names and values.
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globalThis.obj2 = { undefined: "undefined", undef: undefined };
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// Dynamically created attribute names and values.
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globalThis.obj3 = new Proxy(new Map(), {
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get(map, name) {
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if (!map.has(name)) {
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console.log("creating attribute", name);
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map.set(name, name);
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}
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return map.get(name);
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},
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});
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mp.runPython(`
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import js
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print(js.obj1.a, js.obj1.b)
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print(js.obj1["a"], js.obj1["b"])
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print(js.obj2.undefined, js.obj2.undef)
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print(js.obj3.c)
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print(js.obj3["c"])
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print(hasattr(js.obj3, "d"))
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print(js.obj3.d)
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`);
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