Rust Serdeの、Serialize / Deserialize でjavascript変数を渡し、戻り値を取得

lib.rs

// [dependencies]
// wasm-bindgen = { version = "0.2", features = ["serde-serialize"] }
// serde = { version = "1.0", features = ["derive"] }

use serde::{Deserialize, Serialize};
use std::collections::HashMap;

#[derive(Serialize, Deserialize)]
pub struct Example {
    pub field1: HashMap<u32, String>,
    pub field2: Vec<Vec<f32>>,
    pub field3: [f32; 4],
    pub field4: String,
}

#[wasm_bindgen]
pub fn send_example_to_js() -> JsValue {
    let mut field1 = HashMap::new();
    field1.insert(0, String::from("ex"));
    let example = Example {
        field1,
        field2: vec![vec![1., 2.], vec![3., 4.]],
        field3: [1., 2., 3., 4.],
        field4: "f4".to_string()
    };

    JsValue::from_serde(&example).unwrap()
}

#[wasm_bindgen]
pub fn receive_example_from_js(val: &JsValue, f4_val: &str) -> JsValue {
    let mut example: Example = val.into_serde().unwrap();
    example.field4 = String::from( f4_val) ;
    console::log_1(&JsValue::from_str( &example.field4 ));

    JsValue::from_serde(&example).unwrap()
}

Test.js

// JS
        let d = wasm.send_example_to_js();
        console.log( d )
        let d2 = wasm.receive_example_from_js(d, "f4-from-js")
        console.log( d2 )