Function react_sys::use_effect

pub fn use_effect(
    effect: &Closure<dyn FnMut()>, 
    dependencies: Option<Box<[JsValue]>>
)

React.useEffect(effect, dependencies)

Safety

effect closure will be passed to js runtime and called ( or never called ) asynchronously by React.

As wasm_bindgen describes,

Once a Closure is dropped, it will deallocate its internal memory and invalidate the corresponding JavaScript function so that any further attempts to invoke it raise an exception.

Rust compiler can only ensure this closure is not dropped before use_effect returned, so it’s up to you to make sure the closure lived longer enough to be valid in the component life time.

Thus, this function is marked unsafe as a warning.