Macro lazy_preload 

lazy_preload!() { /* proc-macro */ }

Preloads a lazy function and returns a signal that evaluates to true once the function is loaded.

The first time a signal is created through this macro, the WebAssembly (WASM) binary containing the lazy function will be loaded and ready to call. This can be useful when the WASM binary is big and you want to display a placeholder view while it is loading.

When called from a server, the signal returned by lazy_preload will always return false to match with the client’s expectation on first render.

Only a function marked as #[lazy] can be passed to lazy_preload.

#[lazy]
fn lazy_func() {}

fn preload_lazy() -> &'static str {
    let is_loaded = lazy_preload!(lazy_func);
    if is_loaded.get() {
        "Loaded"
    } else {
        "Loading..."
    }
}

mod scoped {
    #[lazy]
    pub fn lazy_func() {}
}

// Also works with scoped lazy functions
fn preload_scoped_lazy() {
    let is_loaded = lazy_preload!(scoped::lazy_func);
}