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. wasm-bindgen
will bind a JsStatic
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_variables)] #fn main() { #[wasm_bindgen] extern "C" { #[wasm_bindgen(thread_local)] 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_variables)] #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, js_name = namespace)] static NAMESPACE: JsValue; // Refer to SomeType's class #[wasm_bindgen(thread_local, 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_variables)] #fn main() { #[wasm_bindgen] extern "C" { #[wasm_bindgen(thread_local, static_string)] static STRING: JsString = "a string literal"; } #}