---
title: "use_callback"
---

`use_callback` is used for obtaining an immutable reference to a memoized `Callback`.
Its state persists across renders.
It will be recreated only if any of the dependencies values change.

`use_callback` can be useful when passing callbacks to optimized child components that rely on
PartialEq to prevent unnecessary renders.

```rust
use yew::prelude::*;

#[derive(Properties, PartialEq)]
pub struct Props {
    pub callback: Callback<String, String>,
}

#[function_component(MyComponent)]
fn my_component(props: &Props) -> Html {
    let greeting = props.callback.emit("Yew".to_string());

    html! {
        <>{ &greeting }</>
    }
}

#[function_component(UseCallback)]
fn callback() -> Html {
    let counter = use_state(|| 0);
    let onclick = {
        let counter = counter.clone();
        Callback::from(move |_| counter.set(*counter + 1))
    };

    // This callback depends on (), so it's created only once, then MyComponent
    // will be rendered only once even when you click the button mutiple times.
    let callback = use_callback(
        move |name| format!("Hello, {}!", name),
        ()
    );

    // It can also be used for events.
    let oncallback = {
        let counter = counter.clone();
        use_callback(
            move |_e| (),
            counter
        )
    };

    html! {
        <div>
            <button {onclick}>{ "Increment value" }</button>
            <button onclick={oncallback}>{ "Callback" }</button>
            <p>
                <b>{ "Current value: " }</b>
                { *counter }
            </p>
            <MyComponent {callback} />
        </div>
    }
}
```