Macro wasm_error 

macro_rules! wasm_error {
    (
        $(#[$meta:meta])*
        $vis:vis enum $name:ident {
            $(
                $(#[$vmeta:meta])*
                $variant:ident($inner:ty) => $js_name:literal
            ),+ $(,)?
        }
    ) => { ... };
}

Define a WASM error enum with Display, From<Self> for JsValue, and From<serde_wasm_bindgen::Error>.