By default, Rust exports exposed to JavaScript will generate TypeScript definitions (unless --no-typescript is used). The skip_typescript attribute can be used to disable type generation per function, enum, struct, or field. For example:

# #![allow(unused_variables)]
#fn main() {
#[wasm_bindgen(skip_typescript)]
pub enum MyHiddenEnum {
    One,
    Two,
    Three
}

#[wasm_bindgen]
pub struct MyPoint {
    pub x: u32,

    #[wasm_bindgen(skip_typescript)]
    pub y: u32,
}

#[wasm_bindgen]
impl MyPoint {

    #[wasm_bindgen(skip_typescript)]
    pub fn stringify(&self) -> String {
        format!("({}, {})", self.x, self.y)
    }
}
#}

Will generate the following .d.ts file:

/* tslint:disable */
/* eslint-disable */
export class MyPoint {
  free(): void;
  x: number;
}

When combined with the typescript_custom_section attribute, this can be used to manually specify more specific function types instead of using the generated definitions.