Getting an array in Javascript from Rust compiled in Emscripten

Question

I want to create a byte vector ( Vec<u8>in Rust) and access it using JS like Arrayor Uint8Arrayand send it to WebSocket or to IndexedDB.

I found How to pass an array from JavaScript to Rust that was compiled using Emscripten? , which is the exact opposite of what I would like to do, but very relevant. Other than that, I know the type of the array in Emscripten, but I don't know how to use it correctly.

My best guess on how to do this is to try to return the vector as_mut_ptrand use a pointer to Module.HEAPU8.

main.rs

#[no_mangle]
pub fn bytes() -> *mut u8 {
    vec![1, 2, 3].as_mut_ptr()
}

fn main() {}

The index.html part

var Module = {
    wasmBinaryFile: "site.wasm",
    onRuntimeInitialized: main,
};
function main() {
    let ptr = Module._bytes();
    console.log(ptr);
    console.log(Module.HEAPU8.slice(ptr, ptr + 10));
    console.log(Module.HEAPU8.subarray(ptr, ptr + 100));
    let arr = Module.cwrap('bytes', 'array', []);
    console.log(arr());
}

The console results ended as follows:

5260296  site:11:13
Uint8Array [ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 ]  site:12:13
Uint8Array [ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 90 more… ]  site:13:13
5260296  site:15:13

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Answer 1

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Answer 2

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