this

Typically, this bindings are achieved via impl block definitions for methods.

But since all regular JavaScript functions may accept arbitrary this bindings, it is possible to support this as well for free functions.

The #[wasm_bindgen(this)] attribute can be applied to exported Rust functions to make them receive the JavaScript this value as their first parameter. This allows creating functions that can be called with .call() or .apply() to set the this context.

#![allow(unused)]
fn main() {
use wasm_bindgen::prelude::*;

#[wasm_bindgen(this)]
pub fn get_property(this: &JsValue, property: &str) -> JsValue {
    js_sys::Reflect::get(this, &property.into()).unwrap()
}

#[wasm_bindgen(this)]
pub fn add_to_count(foo: &JsValue, value: u32) -> u32 {
    let current = js_sys::Reflect::get(foo, &"count".into())
        .unwrap()
        .as_f64()
        .unwrap() as u32;
    current + value
}
}

With the above called via get_property.call({ str: 'foo' }, 'str') or add_to_count.apply({ count: 1 }, [7]) respectively.

Can only be used on functions, not methods or static methods within impl blocks, and the function must have at least one parameter.