Importing a js function with an object parameter - Rust / wasm_bindgen

Question

I'm trying to use a JS function from within rust with wasm_bindgen, the function has an object parameter similar to functions like fetch:

#[wasm_bindgen]
extern "C" {
    #[wasm_bindgen]
    fn fetch(resource: &str, config: &JsValue);
}

(just using fetch as an example, I know that there are better ways to use fetch from rust...)

I'm not sure how to model the config object in rust.

I tried using JsValue but it seems that JsValue can only be created from primitive types and not from objects.

I've seen online some suggestions that serde can help here but I couldn't find any concrete examples, and my attempt to get it to work myself were not fruitful either.

Thanks in advance for looking into this!

transistor · Accepted Answer · 2021-03-31 18:43:37Z

It looks like you can either use js_sys::Reflect to access or set arbitrary values, or you can use serde to parse/unparse values

For the first method, this resource explains how to read or write a property on an untyped object: https://rustwasm.github.io/docs/wasm-bindgen/reference/accessing-properties-of-untyped-js-values.html and an example of using this interface can be found in web-sys itself, which defines the RequestInit object which is used when building the config object for fetch(): https://docs.rs/web-sys/0.3.50/src/web_sys/features/gen_RequestInit.rs.html#4

The other way is to use serde. An example of this can be found at https://rustwasm.github.io/docs/wasm-bindgen/examples/fetch.html and a more detailed explanation can be found at https://rustwasm.github.io/docs/wasm-bindgen/reference/arbitrary-data-with-serde.html

After defining the objects to serialize and deserialize, the JsValue::from_serde() and .into_serde() can be used to convert to and from a JsValue

Mendy · Accepted Answer · 2021-04-01 10:14:36Z

0

Another option a colleague pointed out is using serde_wasm_bindgen, E.g.

#[derive(Serialize, Deserialize)]
struct FetchConfig {
    pub method: String,
}

fn call_fetch() {
    let config = FetchConfig {
        method: "post".to_string()
    };
    let config = serde_wasm_bindgen::to_value(&config).unwrap();
    fetch("https://example.com", &config);
}

answered Apr 1, 2021 at 10:14

Mendy

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