Use of static to Access JS Objects

JavaScript modules will often export arbitrary static objects for use with their provided interfaces. These objects can be accessed from Rust by declaring a named static in the extern block with an #[wasm_bindgen(thread_local_v2)] attribute. wasm-bindgen will bind a JsThreadLocal for these objects, which can be cloned into a JsValue. For example, given the following JavaScript:

let COLORS = {
    red: 'rgb(255, 0, 0)',
    green: 'rgb(0, 255, 0)',
    blue: 'rgb(0, 0, 255)',
};

static can aid in the access of this object from Rust:

#![allow(unused)]
fn main() {
#[wasm_bindgen]
extern "C" {
    #[wasm_bindgen(thread_local_v2)]
    static COLORS;
}

fn get_colors() -> JsValue {
    COLORS.with(JsValue::clone)
}
}

Since COLORS is effectively a JavaScript namespace, we can use the same mechanism to refer directly to namespaces exported from JavaScript modules, and even to exported classes:

let namespace = {
    // Members of namespace...
};

class SomeType {
    // Definition of SomeType...
};

export { SomeType, namespace };

The binding for this module:

#![allow(unused)]
fn main() {
#[wasm_bindgen(module = "/js/some-rollup.js")]
extern "C" {
    // Likewise with the namespace--this refers to the object directly.
    #[wasm_bindgen(thread_local_v2, js_name = namespace)]
    static NAMESPACE: JsValue;

    // Refer to SomeType's class
    #[wasm_bindgen(thread_local_v2, js_name = SomeType)]
    static SOME_TYPE: JsValue;

    // Other bindings for SomeType
    type SomeType;
    #[wasm_bindgen(constructor)]
    fn new() -> SomeType;
}
}

Static strings

Strings can be imported to avoid going through TextDecoder/Encoder when requiring just a JsString. This can be useful when dealing with environments where TextDecoder/Encoder is not available, like in audio worklets.

#![allow(unused)]
fn main() {
#[wasm_bindgen]
extern "C" {
    #[wasm_bindgen(thread_local_v2, static_string)]
    static STRING: JsString = "a string literal";
}
}
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